Zn含量对Mg-xZn-3Y-0.7Zr合金组织和性能的影响

Influence of Zn Content on Microstructure and Mechanical Properties of Mg-xZn-3Y-0.7Zr Alloys

采用低压铸造制备了Mg-xZn-3Y-0.7Zr合金,利用金相显微镜、扫描电镜、能谱分析仪、热分析仪等设备,研究了Zn含量对合金微观组织的影响,并通过热处理工艺来改善合金微观组织中的第二相分布,从而提高合金的力学性能。结果表明,Mg-5Zn-3Y-0.7Zr合金主要含有α-Mg和W-Mg3Zn3Y2相,其中W相呈网状在晶界上分布;当Zn含量为8%时,铸态组织中树枝晶明显增多,并且出现了I-Mg3Zn6Y相;热处理后I相消失,网状分布的W相被打断,在三角晶界处仍有鱼骨状片层共晶组织。Mg-5Zn-3Y-0.7Zr合金铸态抗拉强度、屈服强度和伸长率分别为223.8MPa、124.9MPa和7.3%,经过T6处理后提升效果不明显,而Mg-8Zn-3Y-0.7Zr合金在铸态时力学性能较差,经过T6处理后其抗拉强度、屈服强度和伸长率为263.3 MPa、207.9 MPa和2.2%。Mg-5Zn-3Y-0.7Zr合金的断裂机制为准解理断裂,断口处有发生塑性变形而出现的撕裂棱。Mg-8Zn-3Y-0.7Zr合金的断裂机制主要为解理断裂,并没有发现韧窝。

Mg-xZn-3 Y-0.7 Zr alloy was prepared by low-pressure casting.Evolution of the microstructure of Mg-xZn-3 Y-0.7 Zr alloy was observed by optical microscope,scanning electron microscope and differential thermal analysis.The heat treatment process was optimized to improve the mechanical properties through controlling secondary phase distribution in the Mg alloy.The results indicate that the as-cast microstructure of Mg-5 Zn-3 Y-0.7 Zr alloy is composed ofα-Mg and W-Mg3 Zn3 Y2 phase.The W phase with net-like structure is distributed along the grain boundary.With the addition of 8% Zn,dendrites in as-cast alloy are obviously increased,and I-Mg3 Zn6 Y phase appears.After T6 heat treatment,the IMg3 Zn6 Y phase disappears,and the plate-like eutectic structure of W phase is broken,however,fishbone lamellar eutectic structure is reserved at triangle grain boundary.The tensile test shows that the ultimate tensile strength,yielding strength and elongation of as-cast Mg-5 Zn-3 Y-0.7 Zr alloy reach 223.8 MPa,124.9 MPa and 7.3%,respectively.Effects of T6 heat treatment on mechanical properties of the Mg-5 Zn-3 Y-0.7 Zr alloy can be ignored.After T6 heat treatment,the mechanical properties of Mg-8 Zn-3 Y-0.7 Zr alloy are improved greatly.The ultimate tensile strength,yielding strength and elongation reach 263.3 MPa,207.9 MPa and 2.2%,respectively.The fracture mechanism of Mg-5 Zn-3 Y-0.7 Zr is characterized by quasi cleavage crack with tearing ridge,while the Mg-5 Zn-3 Y-0.7 Zr alloy is characterized by cleavage fracture with absence of dimple.