Influences of Quench Cooling Rate on Microstructure and Corrosion Resistance of Al-Cu-Mg Alloy Based on the End-Quenchin
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THE excellent mechanical properties of Al-Cu-Mg alloy make it the material of choice that is extensively applied in the aerospace and automotive fields. The alloy is ordinarily supplied as T351 or T851 to manufacture large pieces such as aircraft wings or skin.[1–3] In general, the thickness of an Al-Cu-Mg alloy plate could be up to 120 to 150 mm.[4] Due to this thickness, heat transfer is slower inside the plate than on the surface during quenching process. This difference can result in an inhomogeneous distribution of temperature field and create the hardenability problem.[5] The difference in quench cooling rate creates nonuniform microstructures and properties at different cooling distances. Furthermore, the hardenability is incapable of improving, even if the quench cooling rate increases. The end-quenching test (Jominy test) has been widely used to investigate the hardenability of aluminum alloy.[5–7] Combined with quenching factor analysis (QFA) method, the performance of alloys that underwent different cooling rates can be predicted.[8] The majority of researchers have focused on the prediction YUAN YIN, BINGHUI LUO, HUIBO JING, ZHENHAI BAI, and YANG GAO are with the School of Materials Science and Engineering, Central South University, Changsha 410083, Hunan Province, P.R. China. Contact e-mail: [email protected] Manuscript submitted October 16, 2017.
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of mechanical properties such as hardness and strength. Dae-Hoon Ko investigated the validity of hardness prediction of hot-stamped parts based on the quenching factor method; the predictions exhibited a maximum error of 4.96 percent, and excellent agreement was observed between the predicted and measured values.[9] Shu-Hui Ma attempted to simulate a Jominy test of cast aluminum alloy A356 with the QFA method; additionally, the mechanical properties affected by quenching rates were predicted, and kinetic parameters were estimated.[10] Murat Tiryakiog˘lu proposed an effective model suitable for the prediction of tensile strength in a cast Al-Mg-Si alloy.[11] Marco. J. Starink established a model for precipitating reactions during the cooling of Al-Zn-Mg-Cu-based alloys, and the strength after an artificial aging treatment was predicted and verified through an extensive set of cooling experiments.[12] However, few studies have focused on the relationship between cooling rate and corrosion resistance of aluminum alloys based on the end quenching experiments. Dong-Feng Li analyzed the microstructures at different positions of Jominy sample, and the exfoliation corrosion sensitivity of Al-Zn-Mg-Cu alloy was studied under different cooling rates.[13] Liu combined the cooling rate with an electrochemical impedance spectroscopy test and accelerated immersion experiment to investigate the relation between quenching rate and exfoliation corrosion resistance of 7055 aluminum alloy. The results indicated that a slower quench rate leads to lower exfoliation corrosion resistance.[14] Comparatively, other researchers have investig
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