Effects of Bi on the microstructure and mechanical property of ZK60 alloy

Microstructures and phase compositions of as-cast and extruded ZK60-xBi (x = 0–1.64) alloys were investigated. Meanwhile, the tensile mechanical property and hardness were tested. With increasing the Bi content, the as-cast microstructure is first refined obviously, and then becomes coarse slightly. New small block compound which is rich in Zr, Zn, Bi and poor in Mg increases gradually, and MgZn2 phase decreases gradually. The second phase mainly precipitates along the grain boundary. The as-cast tensile mechanical property is first enhanced obviously, where the tensile strength σb, yield strength σ0.2 and elongation δ can reach 265 MPa, 151 MPa and 13.5% for ZK60-0.23Bi alloy, respectively, then remains the high value for ZK60-(0.37–1.09)Bi alloys, and finally decreases obviously for ZK60-1.64Bi alloy. After hot extrusion, the obvious dynamic recrystallization occurs. Broken block compound distributes along the extrusion direction by zonal shape. The average grain size can reach only 4–6 μm. The extruded tensile mechanical property is enhanced significantly, where σb, σ0.2 and δ are at the range of 345–360 MPa, 285–300 MPa and 15.5–19.5%, respectively. Extruded tensile fracture exhibits a typical character of ductile fracture.