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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 alloy automobile engine cylinder liner with the same composition and different microstructures was prepared by metal gravity casting and squeeze casting, respectively. The in-situ tensile test was used to study the crack initiation and Extended behavior. The experimental results show that in the alloyed samples of metal casting, the microcracks initially originated on the primary Si, but did not extend to the matrix. The initiation of the primary crack originated from the deformation of the shear band of the matrix, with a large aspect ratio The main crack of the crystal Si provides a rapid expansion channel, that is, the eutectic Si having a larger aspect ratio is more likely to expand the primary crack than the primary Si. In the sample of the squeeze cast alloy, the initial microcracks also initiate on the primary Si, However, these micro-cracks extended to the matrix and connected to each other as a main crack. In addition, the micro-cracks in the squeeze cast alloy hardly appeared on the spherical eutectic Si, and the penetration of primary Si by the main crack was more common. The analysis results show that the size and shape distribution of Si and eutectic Si in hypereutectic Al-Si alloy need to be matched and coordinated with each other to get better mechanical properties.