GWN751K镁合金组织和性能研究

Study on the Microstructures and Properties of GWN751K Magnesium Alloy

摘要:

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=215 MPa，σ0.2=187 MPa，δ=3.5%，DSC曲线存在明显的低熔点吸热峰；经过535 ℃，16 h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=240 MPa，σ0.2=189 MPa，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=320 MPa，σ0.2=260 MPa，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400 MPa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 ℃，16 h热处理以及挤压后的合金二次裂纹主要是在晶粒内部。

Abstract:

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.