Faculty Profiles - OKAYASU Mitsuhiro

Papers - OKAYASU Mitsuhiro

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Mechanical properties and failure characteristics of cast and extruded Mg97Y2Zn1 alloys with LPSO phase

Mitsuhiro Okayasu, Shuhei Takeuchi, Masafumi Matsushita, Naoya Tada, Michiaki Yamasaki, Yoshihito Kawamura

Materials Science and Engineering A 652 ( Jan. ) 14 - 29 2016.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

Mechanical properties and failure characteristics of Mg97Y2Zn1 (at%) alloys, prepared by gravity casting and extrusion processes, are examined experimentally. High tensile and fatigue strengths are obtained for extruded Mg97Y2Zn1 alloys, with the values being approximately twice as high as those for cast Mg97Y2Zn1 alloys. Such high strengths are attributed to the high internal stress arising from the complicated microstructure and severe lattice strain in the alpha-Mg and long-period stacking order phases. On the other hand, a high fracture strain is obtained for cast Mg97Y2Zn1 alloy, which is affected not only by the lower internal stress, but also severe kink deformation. The failure characteristics, e.g., crack growth characteristics are examined via direct observation during tensile and fatigue tests at micro- and nano-scales. Meandering fatigue crack growth is obtained for the cast Mg97Y2Zn1 alloys. The mean roughness of the fracture surface for cast Mg97Y2Zn1 alloys is more than twice as high as that for commercially available AM60 and AZ91 cast alloys. A coarse fracture surface that was observed in the cast Mg97Y2Zn1 alloys would make severe roughness-induced crack closure, leading to high fatigue strength. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2015.11.069

Material properties of Al-Si-Cu aluminium alloy produced by the rotational cast technology

M. Syahid, M. Okayasu, S. Wu

International Journal on Smart Material and Mechatronics 3 ( 1 ) 145 - 151 2016

The electric power generation characteristics of a lead zirconate titanate piezoelectric ceramic under various cyclic loading conditions

Mitsuhiro Okayasu, Keisuke Watanabe

Ceramics International 41 ( 10 ) 15097 - 15102 2015.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

The electric power generation properties of lead zirconate titanate (PZT) ceramic have been studied under various cyclic loading conditions. The maximum electric voltage increases with an increase in the frequency under the triangular and sinusoidal wave modes, whereas the voltage decreases with an increase in the frequency for the square wave mode. The maximum electric voltage for all wave modes is saturated at around 15 Hz, namely, the electric voltage for the three wave modes is almost constant even if the frequency increases by more than 15 Hz. With an increase in the loading frequency (50 Hz) under the square and triangular wave modes, the electric voltage generates a sinusoidal-like curve formation, which is not reflected by the loading wave mode. The electric voltage increases with an increase of the frequency for the triangular and sinusoidal wave modes, because of the high kinetic energy. For the square wave formation especially at high frequency, a low electric voltage is obtained, which is caused by the switching back of the electric generation arising from the rapid loading speed. The electric voltage increases non-linearly with increasing loading value, and the voltage values become almost constant when loaded with more than 10 N because of the limitation of the amount of electrons in the PZT ceramic. In the early loading stage, the electric voltage values do not increase with high efficiency, in which case the weak fitting of the PZT ceramic plate to the test fixture is affected. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

DOI： 10.1016/j.ceramint.2015.08.076

The Effects of Defects on Tensile Properties of Cast ADC12 Aluminum Alloy

Mitsuhiro Okayasu, Hikoyuki Sakai

Metallurgical and Materials Transactions A 46A ( 11 ) 5418 - 5430 2015.11

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

To better understand the effects of cast defects on mechanical properties, cast aluminum alloys with various porosities were used. Porosity in the cast samples was created during the casting process, and to clearly identify the porosity effects on the mechanical properties, artificial defects (porosity-like tiny holes) were created mechanically. The tensile properties for the cast aluminum alloys appear to be attributed to the area fraction of the porosity on the fracture surface (namely, the defect rate, DR), although there were different trends because of the different stress concentrations: the ultimate tensile strength and 0.2 pct proof strength were linearly related to DR, while a non-linear correlation was detected for fracture strain. Even in Al alloys with small amounts of defects, significant reductions in the fracture strain were observed. These results were verified using tensile tests on specimens containing artificial defects. The effects of artificial defects on the tensile properties were further investigated using numerous tiny holes, created in several formations. The artificial defects (several small holes), lined up at perpendicular (90 deg) and 45 deg directions against the loading direction, made significant reductions in the tensile properties, even though only weak defect effects were observed for the 90 deg loading direction. No severe defect effects were obvious for the specimen with a tiny defect of I center dot 0.1 mm, because of the lower stress concentration, compared to the microstructural effects in the cast Al alloys: the grain boundaries and the second phases. Such phenomena were clarified using tensile tests on cast samples with differently sized microstructures. There were no clear defect effects on the yield strength as the defect amount was less than 10 pct, and microstructural effects were not detected either in this case. Failure characteristics during tensile loading were revealed directly by in-situ strain observations using high-speed cameras.(C) The Minerals, Metals & Materials Society and ASM International 2015

DOI： 10.1007/s11661-015-3134-7

Effects of cyclic loading on fatigue properties of austenite stainless steel

Mitsuhiro Okayasu, Hironobu Fukui

Journal of Mechanical Science and Technology 29 ( 9 ) 3663 - 3668 2015.9

Language：English Publishing type：Research paper (scientific journal) Publisher：KOREAN SOC MECHANICAL ENGINEERS

Fatigue properties of stainless steels have been investigated by various researchers. The present work examined fatigue properties under various cyclic loading conditions to determine the significant factors of loading condition to fatigue strength (sigma(e)). From this approach, no clear frequency effects on the S-N (f) relation were detected, but clear R-ratio effects were identified on fatigue strength. A higher R-ratio yielded higher sigma(e), and a clear correlation was observed between R-ratio and endurance limit. A different trend was observed for the S-N (f) curve when the stress value on the ordinate of the S-N f relation was plotted using the maximum tensile stress (sigma(max)). However, the S-N (f) curves obtained overlaid each other when using stress amplitude (sigma(a)) instead of sigma(max). Fatigue properties were analyzed further using several relations proposed previously, such as modified Goodman relation. In this case, the fatigue data obtained were clearly approximated by an elliptical relation. Severe microstructural damage arising from plastic deformation was observed in the sample fractured under the R = -1 condition, where striation was a main failure mode. In contrast, no clear microstructural damages were observed in the samples fractured at R = 0.1 even when a higher maximum tensile stress was applied (e.g., sigma(max) = 60% sigma(UTS)), where ripple-like failure was the dominant feature.

DOI： 10.1007/s12206-015-0810-x

Material Properties of Various Cast Aluminum Alloys Made Using a Heated Mold Continuous Casting Technique with and without Ultrasonic Vibration

Mitsuhiro Okayasu, Yuta Miyamoto, Kazuma Morinaka

Metals 5 ( 3 ) 1440 - 1453 2015.9

Language：English Publishing type：Research paper (scientific journal) Publisher：MDPI AG

This work was carried out to develop high-quality cast aluminum alloys using a new casting technology. For this purpose, commercial Al alloys were created by heated mold continuous casting (HMC) with ultrasonic vibration (UV). With the HMC process, the grain size and the crystal orientation of the Al alloys were controlled, i.e., fine grains with a uniformly organized lattice formation. In addition, an attempt was made to modify the microstructural formation by cavitation. These microstructural characteristics made excellent mechanical properties. Using UV in the continuous casting process, more fine and spherical grains were slightly disordered, which was detected using electron backscattered diffraction. The mechanical properties of the UV HMC Al alloys were slightly higher than those for the related cast Al alloys without UV. Moreover, the severe vibration caused higher mechanical properties. The lattice and dislocation characteristics of the cast samples made with and without UV processes were analyzed systematically using electron backscattered diffraction.

DOI： 10.3390/met5031440

Precise analysis of effects of aging on mechanical properties of cast ADC12 aluminum alloy

Mitsuhiro Okayasu, Shoka Go

Materials Science and Engineering A 638 208 - 218 2015.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

To better understand the effects of aging on mechanical properties of cast Al-Si-Cu-based aluminum alloy (ADC12), artificial aging was carried out under a range of conditions after water quenching. Two casting methods were employed: gravity casting (GC) and heated-mold continuous casting (HMC). The Vickers hardness of GC samples was higher overall than that of HMC samples both before and after aging. This was due to the high solubility of the alloy elements in the alpha-Al matrix and to the presence of complicated dislocation walls in the GC samples. The hardness of GC and HMC samples aged at 433, 448 and 463 K increased similarly with increasing aging time, and an aging peak occurred in the age-hardening curve between 10 and 15 h. In contrast to the hardness results, the ultimate tensile strength (UTS) for the as-cast GC sample was about 30% lower than that for the as-cast HMC sample, because of large brittle eutectic Si and Fe structures. The highest UTS was obtained for the HMC sample aged at 448 K for 13 h, and was about 20% and 10% higher, respectively, than those of the as-cast HMC sample and the GC sample aged at 448 K for 13 h. The high UTS for the HMC sample was due to precipitation of theta' (Al2Cu) metastable phases as well as the formation of tiny microstructures. With over-aging at 463 and 493 K for 100 h, the tensile strength decreased for both GC and HMC samples, although the fracture strain increased only for HMC samples (by more than 30%). Such high ductility in ADC12 alloy has not been seen in previous studies. In contrast, no clear improvement in material ductility was detected in GC samples. The tensile strength was directly related to fatigue properties, although no significant effect of ductility on fatigue strength was found. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2015.04.072

Crystallization characteristics of cast aluminum alloys during a unidirectional solidification process

Mitsuhiro Okayasu, Shuhei Takeuchi

Materials Science and Engineering A 633 ( May ) 112 - 120 2015.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The crystal orientation characteristics of cast Al-Si, Al-Cu and Al-Mg alloys produced by a unidirectional solidification process are examined. Two distinct crystal orientation patterns are observed: uniform and random formation. A uniform crystal orientation is created by columnar growth of alpha-Al dendrites in the alloys with low proportions of alloying element, e.g., the Al-Si alloy (with Si <12.6%) and the Al-Cu and Al-Mg alloys (with Cu and Mg < 2%). A uniformly organized crystal orientation with [100] direction is created by columnar growth of alpha-Al dendrites. With increasing proportion of alloying element (>2% Cu or Mg), the uniform crystal orientations collapse in the Al-Cu and Al-Mg alloys, owing to interruption of the columnar alpha-Al dendrite growth as a result of different dynamics of the alloying atoms and the creation of a core for the eutectic phases. For the hypo-eutectic Al-Si alloys, a uniform crystal orientation is obtained. In contrast, a random orientation can be detected in the hyper-eutectic Al-Si alloy (15% Si), which results from interruption of the growth of the alpha-Al dendrites due to precipitation of primary Si particles. There is no clear effect of crystal formation on ultimate tensile strength (UTS), whereas crystal orientation does influence the material ductility, with the alloys with a uniform crystal orientation being elongated beyond their UTS points and with necking occurring in the test specimens. In contrast, the alloys with a nonuniform crystal orientation are not elongated beyond their UTS points. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2015.03.001

Precise Analysis of Microstructural Effects on Mechanical Properties of Cast ADC12 Aluminum Alloy

Mitsuhiro Okayasu, Shuhei Takeuchi, Masaki Yamamoto, Hiroaki Ohfuji, Toshihiro Ochi

Metallurgical and Materials Transactions A 46A ( 4 ) 1597 - 1609 2015.4

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

The effects of microstructural characteristics (secondary dendrite arm spacing, SDAS) and Si- and Fe-based eutectic structures on the mechanical properties and failure behavior of an Al-Si-Cu alloy are investigated. Cast Al alloy samples are produced using a special continuous-casting technique with which it is easy to control both the sizes of microstructures and the direction of crystal orientation. Dendrite cells appear to grow in the casting direction. There are linear correlations between SDAS and tensile properties (ultimate tensile strength sigma (UTS), 0.2 pct proof strength sigma (0.2), and fracture strain epsilon (f)). These linear correlations, however, break down, especially for sigma (UTS) vs SDAS and epsilon (f) vs SDAS, as the eutectic structures become more than 3 mu m in diameter, when the strength and ductility (sigma (UTS) and epsilon (f)) decrease significantly. For eutectic structures larger than 3 mu m, failure is dominated by the brittle eutectic phases, for which SDAS is no longer strongly correlated with sigma (UTS) and epsilon (f). In contrast, a linear correlation is obtained between sigma (0.2) and SDAS, even for eutectic structures larger than 3 mu m, and the eutectic structure does not have a strong effect on yield behavior. This is because failure in the eutectic phases occurs just before final fracture. In situ failure observation during tensile testing is performed using microstructural and lattice characteristics. From the experimental results obtained, models of failure during tensile loading are proposed. (C) The Minerals, Metals & Materials Society and ASM International 2015

DOI： 10.1007/s11661-015-2747-1

Influence of solidification rate on material properties of cast aluminium alloys based on al-si-cu and al-si-mg

M. Okayasu, S. Yoshida

International Journal of Cast Metals Research 28 ( 2 ) 105 - 116 2015.4

Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD

Material properties of two different aluminium alloys (ADC12 and AC4C) were investigated using cast samples produced by conventional gravity and pressure casting at various solidification rates. The microstructural characteristics and defect density vary depending on the cast sample. Those material characteristics affect directly the mechanical properties. The mechanical properties, including tensile strength and fatigue strength, are improved with increasing solidification rate, due to the fine grains, very small eutectic structures and low dislocation density. Tensile strength and ductility for the AC4C alloy are overall higher than those for the ADC12 alloy. The reason for this is attributed to mainly the lower volume fraction of brittle Si- and Fe-based eutectic structures. The mechanical properties are more sensitive to the eutectic structures than to the grain size, although both factors affect the properties significantly. Dimple based ductile fracture is the main feature for the AC4C alloy, while cleavage based brittle failure is the dominant feature for the ADC12 alloy. Severe lattice strain occurs around the cracks in the AC4C alloy because of the high ductility, whereas weak lattice strain occurs in the brittle ADC12 alloy. On the basis of the microstructural and defect characteristics of the cast aluminium alloys, their tensile properties could be approximated using a proposed formula.

DOI： 10.1179/1743133614Y.0000000128

Effects of Stress Concentration on the Mechanical Properties of Carbon Fiber Reinforced Plastic

R. Naito, M. Okayasu, D. Fukuyama

International Journal on Smart Material and Mechatronics 2 ( 2 ) 136 - 139 2015

Mechanical Properties of Samurai Swords (Carbon Steel) Made Using a Traditional Steelmaking Technology (tatara)

M.Okayasu, H.Sakai, T.Tanaka

Journal of Material Sciences & Engineering 4 ( 2 ) 1 - 6 2015

Mechanical Strength and Failure Characteristics of Cast Mg-9 pctAl-1 pctZn Alloys Produced by a Heated-Mold Continuous Casting Process: Tensile Properties

Mitsuhiro Okayasu, Shuhei Takeuchi, Hiroaki Ohfuji

METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 45A ( 12 ) 5767 - 5776 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

The mechanical properties and failure characteristics of a cast Mg alloy (AZ91: Mg-Al-8.9-Zn-0.6-Mn-0.2) produced by a heated-mold continuous casting process (HMC) are investigated. In a modification of the original HMC process, the cooling of the liquid alloy by direct water spray is carried out in an atmosphere of high-purity argon gas. The HMC-AZ91 alloy exhibits excellent mechanical properties (high strength and high ductility) that are about twice as high as those for the same alloy produced by conventional gravity casting. The increased material strength and ductility of the HMC sample are attributed to nanoscale and microscale microstructural characteristics. The fine grains and tiny spherical eutectic structures (e.g., Mg17Al12 and Al6Mn) distributed randomly in the matrix of the HMC alloy result in resistance to dislocation movement, leading to high tensile strength. Basal slip on (0001) planes in the relatively organized crystal orientation of the HMC alloy, as well as grain boundary sliding through tiny spherical eutectic structures, results in high ductility. Details of the failure mechanism under static loading in the HMC alloy are also discussed using failure models.

DOI： 10.1007/s11661-014-2497-5

In Situ Observation of Material Failure in Cast Aluminum Alloy During Monotonic Loading Observed by a High-Speed Camera

M. Okayasu, S. Takeuchi, K. Aizawa

Experimental Mechanics 54 ( 8 ) 1479 - 1489 2014.9

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

In situ observation of the failure characteristics of a cast aluminum alloy has been conducted using a testing system with a high-speed camera. The failure process of the cast Al alloy was captured clearly with an high image resolution (1,024 × 1,024 pixels) at a high frame rate (20,000/s), where the specimen surface for observation was dyed dark using a black oil-based ink. A dark curtain was set behind the test specimen as background. Strong lighting of about 10 klx was used, which was applied to the dark specimen surface for clarification of material failure. The aim of this approach was to detect the failure characteristics or failure objects with bright zone. Using this system, both debris particles flying from the fracture sample and dislocation-like movements were detected. These were observable as tiny bright dots. The flying debris particles of about 35 μm in diameter consisted mainly of Si- and Fe-based eutectic structures. The flying speed of the debris particles was about 1,800 mm/s and their flight distance from the specimen was about 100 mm. The velocity of the dislocation-like movements was found to be less than 1,000 mm/s, and this motion was seen repeatedly before and after sample failure occurred.

DOI： 10.1007/s11340-014-9913-z

Characteristics of electrical power generation from lead zirconate titanatepiezoelectric ceramics under cyclic loading

Mitsuhiro Okayasu, Mamoru Mizuno, Tetsuro Shiraishi

Ceramics International 40 ( 5 ) 6589 - 6595 2014.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

The influence of oscillation condition on the electrical power generation properties of lead zirconate titanate (PZT) piezoelectric ceramics is investigated. It is found that the power generation increases with an increase of both applied load and load frequency. At lower loading frequencies, e.g., 0.1 and 0.5 Hz, the voltage rises instantly to the maximum level under square-wave mode, although the voltage increases gradually under triangular-wave mode. After this initial increase, there is a rapid fall to zero, followed by generation of increasingly negative voltage as the applied load is removed for both wave modes. Variation of the voltage is reflected by the cyclic loading at higher loading frequencies, 15 and 30 Hz. On the basis of the obtained experimental results for the two wave modes, the electrical power generation characteristics of PZT ceramics are proposed, and the voltages generated during loading and unloading are accurately estimated by numerical analysis. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

DOI： 10.1016/j.ceramint.2013.11.114

Mechanical strength and failure characteristics of cast Mg-9%Al-1%Zn alloys produced by a heated-mold continuous casting process: Fatigue properties

Mitsuhiro Okayasu, Shuhei Takeuchi

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 600 211 - 220 2014.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The fatigue properties and failure characteristics of a cast Mg alloy (AZ91: Mg-Al-8.9-Zn-0.6-Mn-0.2) produced by heated-mold continuous casting (HMC) and conventional gravity casting (GC) are investigated. Excellent fatigue properties are obtained for the HMC alloy compared with the GC alloy. The high fatigue strength of the HMC alloy is a reflection of its improved microstructural characteristics, namely, tiny alpha-Mg grains and fine spherical eutectic structures (beta-Mg17Al12). Fatigue cracks propagate mainly in the alpha-Mg grains and along high-hardness beta-phases in both alloys. The direction of fatigue crack growth is altered as the crack reaches the eutectic phases. Because the tiny eutectic phases are distributed randomly in the HMC alloy, a meandering crack path is formed, which results in high crack growth resistance, leading to the high fatigue strength. For the HMC alloy, a striation-like failure mode can be seen in the crack growth stage, and dimple fracture is the dominant feature in the final failure stage. On the other hand, cleavage-like brittle failure with many microcracks can occur in the GC alloy. Severe lattice strain occurs during the final failure stage, especially for the HMC alloy, resulting in strong work hardening, although this is weak in the crack growth site. Severe strain is distributed uniformly around the entire cracks in the HMC alloy when the sample is fractured by monotonic loading. The lattice strains in the HMC alloy under monotonic and cyclic loading are overall higher than those in the GC alloy, owing to the high material ductility of the HMC alloy. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2014.01.098

Strain induced martensite formation characteristics of austenite stainless steel during various loading conditions

M. Okayasu, H. Fukui, H. Ohfuji, T. Shiraishi

Materials Science and Technology (United Kingdom) 30 ( 3 ) 301 - 308 2014.3

Language：English Publishing type：Research paper (scientific journal) Publisher：MANEY PUBLISHING

The strain induced martensitic transformation (SMT) of the austenite stainless steel (SUS 304) under cyclic loading and static loading was investigated directly using electron backscattered diffraction. Two different SMT characteristics are observed, which are attributed to the differences of plastic and twinning deformation. The maximum cyclic stress has a strong influence on the SMT. The total area fraction of the Fe-α' phase increases significantly when the maximum cyclic load is >80% σ . In other words, the SMT is apparently absent when the samples are loaded with less than σ =70% σ , although such samples are fractured completely. Moreover, there is a clear R ratio effect on the SMT. For example, the loading condition R=-1 gives rise to a strong SMT compared to R=0·1 due to the more severe strain caused by the compressive stress. In contrast, no clear frequency effect (1 versus 30 Hz) on the SMT is detected, which may be attributed to the same maximum cyclic stress. Like the SMT characteristics under cyclic loading, the proportion of Fe-α' phase shows no clear increase until the sample is loaded statically to a tensile stress <70% σ . © 2014 Institute of Materials, Minerals and Mining. UTS max UTS UTS

DOI： 10.1179/1743284713Y.0000000353

Influence of microstructural characteristics on mechanical properties of ADC12 aluminum alloy

M. Okayasu, K. Ota, S. Takeuchi, H. Ohfuji, T. Shiraishi

Materials Science and Engineering A 592 189 - 200 2014.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

The effects of microstructural characteristics on the mechanical properties of an aluminum alloy (ADC12: Al-Si -Cu -Zn -Fe -Mg -Mn ) produced by various casting technologies are studied experimentally and numerically. Six different casting processes are employed: gravity casting, cold-chamber die-casting, hot-chamber die-casting, squeeze casting, twin-rolled continuous casting and heated-mold continuous casting. Microstructural characteristics, dislocation density and defect density vary depending on the casting method, owing to differences in solidification rate, casting pressure and injection speed. The material characteristics of the samples affect their mechanical properties. Multiple regression analysis is carried out to find equations to predict tensile strength using five independent factors: secondary dendrite arm spacing, microporosity rate, diameter of eutectic structures, aspect ratio of eutectic structures and dislocation density. All these factors influence the tensile properties, although to different degrees. The estimated values of tensile strength are in good agreement with experimental results. © 2013 Elsevier B.V. 11.3 1.9 0.8 0.8 0.2 0.2

DOI： 10.1016/j.msea.2013.10.098

Effects of loading conditions on the fatigue failure characteristics in a polycarbonate

M. Okayasu, K. Yano, T. Shiraishi

Advances in Materials Research 3 ( 3 ) 163 - 174 2014

Corrosion and mechanical properties of cast aluminium alloys

M. Okayasu, S. Takeuchi, T. Shiraishi

International Journal of Cast Metals Research 26 ( 6 ) 319 - 329 2013.12

Language：English Publishing type：Research paper (scientific journal)

The corrosion and mechanical properties of cast aluminium alloys [ADC6(Al-Mg) and ADC12(Al-Si-Cu)] have been investigated. Specifically, cast samples with different microstructural characteristics were produced using two different casting techniques, namely, gravity casting (GC) and heated mould continuous casting (HMC). For ADC6, intergranular corrosion occurs mainly through the eutectic Mg Si and Al (Mn,Fe) phases and the precipitate free zone around the eutectic structures. On the other hand, pitting corrosion in the α-Al phase is the dominant feature for ADC12. Such corrosion characteristics can be interpreted from the material properties (polarization resistance and electrode potential) of the individual structures, such as the a-Al phase, eutectic a-Al phase and precipitate phase. It also appeared that the extent of corrosion is affected by the size of themicrostructure; the ADC6 sample with small second phases has a high corrosion resistance due to the limited area for corrosion. In addition, the higher proportion of solid solution in the α-Al phase of ADC6, arising from the high cooling rate, makes a high corrosion resistance because of the change of electrode potential. A different trend is obtained for ADC12 due to the pitting corrosion, where low corrosion resistance is obtained for the sample with tiny grain. The tensile strength and ductility for both HMC samples (ADC6 and ADC12) are higher than those for the GC equivalents, which is caused by the presence of tiny microstructures and uniform crystal orientation. However, the mechanical properties of HMC samples decrease dramatically during corrosion, although these are still high compared to those of the GC samples without corrosion. © 2013 W. S. Maney & Son Ltd. 2 6

DOI： 10.1179/1743133613Y.0000000065

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