微量Zr对过共晶Al-20Si合金微观组织和力学性能的影响

Effect of trace zirconium addition on microstructure and mechanical properties of hypereutectic Al-20Si alloy

利用光学显微镜、扫描电镜/能谱、X衍射分析仪及力学性能测试等手段,研究不同添加量的Zr(0.15%,0.3%,0.45%,0.6%)加入Al-20Si合金后对微观组织和力学性能的影响。结果表明:Al-20Si合金中添加微量Zr能使合金中初生硅形态从粗多边形和星形细化为细小多面体形状,并逐渐球化;共晶硅形态从粗大片状、针状结构变为离散颗粒细纤维结构。当Al-20Si合金中的Zr添加量为0.3%时,其细化变质效果最明显,初生硅平均长径比由1.71降至1.26,共晶硅平均长度由20.6μm降至8.7μm。此时,合金的拉伸强度和伸长率分别由初始的89.4MPa和0.67%增至132.1 MPa和1.2%,分别提高了47.8%和79.1%。从XRD和EDS分析结果可知,Al-20Si合金中加入Zr元素形成了Al4Si5Zr3合金相。由断口分析可知,添加Zr形成的Al4Si5Zr3相使合金颗粒弥散并形成了钉扎强化,从而使其力学性能得到显著提升。

In this research,the effects of different zircon additions(0.15%,0.3%,0.45%,0.6%,mass fraction)on the microstructure and mechanic properties of Al-20Si alloy were investigated using OM,SEM/EDS and XRD,and their strength and hardness were measured.The results show that the phenomenon of microstructure modifications are occurred when the zircon is added at trace amount.The coarse polyhedral and star like primary silicon are refined and modified to small polyhedral shape as well as be spherized.When the zircon addition of Al-20Si alloy is 0.3%,the effect of refine and modification is the most obvious.The length-diameter ratio of primary silicon is decreased from 1.71 to 1.26.The coarse silicon with flack/needle shape is changed to fine fiber shape dispersed on the matrix.The length of eutectic silicon decreases from 20.6μm to 8.7μm.From the XRD patterns,the Al4Si5Zr3 phase is formed owing to the zircon addition of Al-20Si alloy.The ultimate tensile strength increases from 89.4 MPa to 132.1 MPa,by 47.8%,and the elongation increases from 0.67%to 1.2%,by 79.1%.From the fracture surface,the promotions of mechanical properties are due to the dispersion and pinning reinforcement caused by the addition of trace zircon.