GWN751K镁合金组织和性能研究

Study on the Microstructures and Properties of GWN751K Magnesium Alloy

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。

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.