工业铸造A357铝合金SEM原位拉伸实验

通过场发射扫描电镜装载原位拉伸台,对不同凝固条件下工业铸造A357铝合金进行原位拉伸试验。结果表明,裂纹微裂纹首先萌生于组织中破裂的共晶硅处,近邻的微裂纹连接形成小裂纹;多处形成的小裂纹彼此连接并形成较长裂纹,沿共晶区深化和扩展,逐渐发展为主裂纹;当主裂纹遇到铝基体时,扩展受阻,裂纹发生钝化并在其前沿区域形成剪切带;剪切带深化并开裂,主裂纹沿着深化的剪切带穿过基体继续扩展,最终导致试样断裂。A357铝合金的断裂方式为兼具韧性断裂和解理断裂的混合断裂。反重力铸造有效地改善合金微观组织形态,提高了合金的力学性能。

In-situ Tension Investigation of Commercial A357 Aluminium Alloys

Two kinds of commercial A357 aluminium alloys solidified under different conditions were studied by carrying out the in-situ tensions experiment on the in-situ loading stage installed in the field emission scanning electron microscope vacuum chamber. The results show that micro-cracks were initiated at cracked eutectic Si particles located in the Al matrix, then adjacent micro-cracks opened, coalesced and at last a small crack was formed; with opening and coalescence of small cracks produced at multiple sites, a longer crack was formed, and this longer crack propagated along eutectic region and finally grew into the main crack; when meeting Al matrix, the main crack stopped and became blunt, forming shear bands afterward; with the shear bands deepened and opened, the main crack continued to propagate along the deepened shear bands, and the specimens were eventually fractured. It was a mixed fracture for the A357 aluminium alloys including both ductile and brittle fracture. In addition, it is found that the microstructure of the alloy in counter-gravity casting is changed, and the mechanical properties is improved.