A390铝合金汽车发动机缸套静载拉伸时的断裂行为  

The Fracture Behaviors of A390 Aluminum Alloys Cylinder Liner under Static Loading

作　　者：李建国[1] 茶国吉[1] 熊守美[2] 韩志强[2] 

机构地区：[1]清华大学材料科学与工程系 [2]清华大学机械工程系

出　　处：《特种铸造及有色合金》2012年第12期1079-1085,共7页Special Casting & Nonferrous Alloys

摘　　要：分别通过金属型重力铸造和挤压铸造制备了成分相同而显微组织不同的A390合金汽车发动机缸套,并用原位拉伸试验法研究了缸套试样在静载拉伸时的裂纹萌生与扩展行为。试验结果表明,在金属型铸造的合金样品中,微裂纹最初萌生于初生Si上,但未扩展到基体上;主裂纹的萌生来源于基体的剪切带变形,具有较大长宽比的共晶Si为主裂纹提供了快速扩展通道,即具有较大长宽比的共晶Si比初生Si更易扩展主裂纹;在挤压铸造的合金样品中,最初的微裂纹同样萌生于初生Si上,但这些微裂纹扩展到基体上并相互连接成为一条主裂纹;此外,挤压铸造合金中的微裂纹几乎不出现在球状共晶Si上,而初生Si被主裂纹穿过的现象更为普遍。分析结果表明,过共晶Al-Si合金中的初生Si和共晶Si的尺寸大小与形貌分布需要合理搭配与相互协调才能获得更好的力学性能。The A390 aluminum alloy cylinder liners were prepared by gravity-casting ana squeeze-casung, and their fracture behaviors under static loading were investigated by in situ SEM observation. For the gravity-casting alloy, microcracks firstly initiated at the primary Si particles however were restricted from propagating to the matrix. Meanwhile, the eutectic Si particles with a high aspect ratio played a bridging role in the dominant crack propagation, which suggested that the eutectic Si particles are more advantageous to crack propagation than primary Si particles in the gravity-casting alloy. By contrast, for the squeeze-casting alloy, microcracks also were observed to initiate firstly at the primary Si particles but then propagate to matrix and link with other microcracks to form a dominant crack. In addition, microc- racks barely initiated at the spherical eutectic Si particles, and the primary Si particles were preferential- ly sought out by the dominant crack. The results indicate that the eutectic Si particles are in competition with primary Si particles in propagating the dominant crack. Moreover, the fracture of eutectic Si parti- cles affect the propagation of microcracks at the primary Si particles due to the function of the eutectic Si particles to release stress. It also suggested that the primary Si particles and eutectic Si particles should be coordinated to achieve excellent mechanical properties of hypereutectic aluminum-silicon alloys.

关 键 词：A390合金 汽车发动机缸套 原位拉伸 断裂行为 初生SI 共晶Si 

分 类 号：TG115.5[金属学及工艺—物理冶金]