汽车用铸造Al-Si合金的热处理与力学性能
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摘要
对铸造Al-7Si-0. 3Mg合金进行了低温拉伸试验,研究了固溶时间对Al-7Si-0. 3Mg合金20、-20和-60℃力学性能和显微组织的影响,并分析了Si相对断裂行为的影响及其作用机理。结果表明:随着固溶时间的延长,合金试样在20、-20和-60℃的屈服强度、抗拉强度和断后伸长率都呈现为先增加而后降低的趋势,在固溶时间为10 h时取得最大值。随着固溶时间的延长,合金中的Si相尺寸和长宽比有所减小,在固溶时间为10 h时,合金中尺寸较小的Si相主要呈现为颗粒状,继续增加固溶时间至15 h时,Si相的尺寸和长宽比增加。随着试验温度的降低,Si相附近的滑移带数量呈现逐渐减少的趋势,较低温度下合金断口附近出现了较多的断裂Si相,但是相对而言,固溶时间为10 h的断裂Si相处的裂纹较小,且断口以小解理平面和韧窝为主,合金韧性相对固溶时间为0 h时更高。在拉伸过程中尺寸较小、圆整度较高的Si相由于位错塞积而产生应力减小,合金更不容易发生断裂。
Low temperature tensile test of cast Al-7 Si-0. 3 Mg alloy was carried out,the effect of solid solution time on the mechanical properties and microstructure of Al-7 Si-0. 3 Mg alloy at 20 ℃,-20 ℃ and-60 ℃ was studied,and the effect of Si phase on fracture behavior and mechanism was analyzed. The results show that with the prolonging of solution treatment time,the yield strength,tensile strength and elongation of the alloy at 20 ℃,-20 ℃ and-60 ℃ first increase then decrease,and get the maximum value when the solution treatment time reaches 10 h. With the prolonging of solution treatment time,the size and the ratio of length to width of Si phase decreases. When the treatment time is 10 h,the smaller Si phase in the alloy is mainly of granular shape; when the treatment time increases to 15 h,both the size and the aspect ratio of Si phase increase. With decreasing of the test temperature,the number of slip bands near the Si phase shows a decreasing trend,and there are more fracture Si phase near the fracture surface at low temperature. However,when the treatment time is 10 h,cracks in the fracture Si phase are smaller,the fracture is dominated by small cleavage plane and dimples,and the toughness of the alloy is higher than than when the treatment time is 0 h. The stress caused by the Si phase with smaller size and higher roundness decreases during tensile test due to dislocation accumulation,and the alloy is less prone to fracture.
Low temperature tensile test of cast Al-7 Si-0. 3 Mg alloy was carried out,the effect of solid solution time on the mechanical properties and microstructure of Al-7 Si-0. 3 Mg alloy at 20 ℃,-20 ℃ and-60 ℃ was studied,and the effect of Si phase on fracture behavior and mechanism was analyzed. The results show that with the prolonging of solution treatment time,the yield strength,tensile strength and elongation of the alloy at 20 ℃,-20 ℃ and-60 ℃ first increase then decrease,and get the maximum value when the solution treatment time reaches 10 h. With the prolonging of solution treatment time,the size and the ratio of length to width of Si phase decreases. When the treatment time is 10 h,the smaller Si phase in the alloy is mainly of granular shape; when the treatment time increases to 15 h,both the size and the aspect ratio of Si phase increase. With decreasing of the test temperature,the number of slip bands near the Si phase shows a decreasing trend,and there are more fracture Si phase near the fracture surface at low temperature. However,when the treatment time is 10 h,cracks in the fracture Si phase are smaller,the fracture is dominated by small cleavage plane and dimples,and the toughness of the alloy is higher than than when the treatment time is 0 h. The stress caused by the Si phase with smaller size and higher roundness decreases during tensile test due to dislocation accumulation,and the alloy is less prone to fracture.
引文
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[2]Mousavi G S,Emamy M,Rassizadehghani J.The effect of mischmetal and heat treatment on the microstructure and tensile properties of A357Al-Si casting alloy[J].Materials Science and Engineering A,2012,556(11):573-581.
[3]Man Z,Jian Z,Yao L,et al.Effect of mischmetal modification treatment on the microstructure,tensile properties,and fracture behavior of Al-7.0%Si-0.3%Mg foundry aluminum alloys[J].Journal of Materials Science,2011,46(8):2685-2694.
[4]吴亮,金青林,蒋业华.铁相形貌对铝硅合金高温拉伸断裂机制的影响[J].材料热处理学报,2013,34(4):51-56.Wu Liang,Jin Qinglin,Jiang Yehua.Effects of iron phase morphology on high temperature tensile fracture behavior of Al-Si alloy[J].Transactions of Materials and Heat Treatment,2013,34(4):51-56.
[5]Lee K,Yong N K,Lee S.Effects of eutectic silicon particles on tensile properties and fracture toughness of A356 aluminum alloys fabricated by low-pressure-casting,casting-forging,and squeezecasting processes[J].Journal of Alloys and Compounds,2008,461(1/2):532-541.
[6]Ravi M,Pillai U T S,Pai B C.The effect of mischmetal addition on the structure and mechanical properties of a cast Al-7Si-0.3Mg alloy containing excess iron(up to 0.6 Pct)[J].Metallurgical and Materials Transactions A,2002,33(2):391-400.
[7]Kunio T,Shimizu M,Yamada K,et al.An effect of the second phase morphology on the tensile fracture characteristics of carbon steels[J].Engineering Fracture Mechanics,1975,7(3):411-417.
[8]Gokhale A M,Dighe M D,Horstemeyer M.Effect of temperature on silicon particle damage in A356 alloy[J].Metallurgical and Materials Transactions A,1998,29:905-907.
[9]Mohamed A M A,Samuel F H,Kahtani S A.Microstructure,tensile properties and fracture behavior of high temperature Al-Si-Mg-Cu cast alloys[J].Materials Science and Engineering A,2013,577:64-72.