GWN751K镁合金组织和性能研究

采用OM,SEM,TEM,XRD等手段,研究了不同状态的GWN751K镁合金的组织和性能。结果表明:铸态合金主要由基体和网状共晶组织构成,σb=215MPa,σ0.2=187MPa,δ=3.5%,DSC曲线存在明显的低熔点吸热峰;经过535℃,16h热处理,共晶组织分解,晶界残留富Mg-Y相,晶粒尺寸明显长大,合金的力学性能有所改善,σb=240MPa,σ0.2=189MPa,δ=10%,DSC曲线低熔点吸热峰消失;合金经过挤压后,发生动态再结晶,力学性能显著提高,σb=320MPa,σ0.2=260MPa,δ=18%,最主要的原因是挤压后合金中存在高密度位错以及细小的晶粒,可显著提高合金的强度和塑性;经过时效后,合金的平均断裂强度达到400MPa以上,但塑性明显降低。铸态合金二次裂纹主要存在于晶界的共晶组织中,535℃,16h热处理以及挤压后的合金二次裂纹主要是在晶粒内部。

Study on the Microstructures and Properties of GWN751K Magnesium Alloy

The microstructures and properties of GWN751K magnesium alloy in different states were investigated by OM, SEM, TEM and XRD. The results show that the microstructure of the as-cast alloy is composed of α-Mg and net-like eutectic phase and σb=215 MPa, σ0.2=187 MPa and δ=3.5% with a low temperature endothermic peak in DSC curve. After 535 oC, 16 h heat treatment, the eutectic structure decomposes and the Mg-Y rich phases remain in the boundary with grains growing up obviously. Mechanical properties become better with σb=240 MPa, σ0.2=189 MPa and δ=10%, and the low temperature endothermic peak disappears. After extrusion, the dynamic recrystallization occurs and as a result the mechanical properties are increased obviously with σb=320 MPa, σ0.2=260 MPa and δ=18%; the main reason is that the high-density dislocation and fine grains can greatly increase the strength and elongation. After aging at 220 oC for 6 h, the average ultimate tensile strength is over 400 MPa but the elongation is decreased sharply. In the as-cast alloy, the secondary cracks were observed along the grain boundaries, mainly at the inside of eutectics. After 535 oC, 16 h heat treatment and extrusion, the secondary cracks mainly locate at the grain interior.