Sc对7056铝合金组织和性能的影响

Effect of Sc on the microstructure and properties of 7056 aluminum alloy

对铸态合金进行了均匀化处理、挤压、固溶处理和时效处理,通过分析合金的化学成分,观察合金在不同状态的显微组织及析出相透射电镜(TEM)形貌,测试合金在热处理后的硬度和拉伸性能,研究了向7056铝合金中加入质量分数0.2%的Sc对合金组织和性能的影响.实验结果表明,Sc元素的加入可以明显细化组织晶粒,铸态晶粒由100~500μm下降到50μm左右;Sc元素的加入对合金的塑性有大幅度提高,时效处理后,合金的断后伸长率从10.82%增加到了13.60%;但屈服强度却由668 MPa下降到657 MPa.通过综合计算晶粒大小、析出相强化等因素,详细分析了Sc元素加入引起7056铝合金峰时效态屈服强度下降的原因.理论计算显示,向合金中加入质量分数0.2%的Sc元素时,峰时效处理后,合金的强度值会下降12.005MPa,与试验值11 MPa接近.研究得到7056铝合金最佳的单级时效制度为120℃+16 h,峰值硬度和强度为195.2 HV和714MPa,此时合金中主要强化相为圆盘状和短棒状的MgZn2相,大小约为4~6 nm,同时存在球状的Al3Zr相,大小约为20 nm.

Al-Zn-Mg-Cu alloys are widely used due to their excellent properties.For the 7056 aluminum alloy developed on the basis of 7055 aluminum alloy,exploring its aging characteristics and the effects of rare earth elements on its microstructure and mechanical properties has a great significance to promote the use of the alloy.In this paper,the as-cast alloy is subjected to homogenization treatment,extrusion,solution treatment,and aging treatment.The effect of adding 0.2%Sc to the 7056 aluminum alloy on the microstructure and properties of the alloy was investigated by analyzing the chemical composition of the alloy,observing the microstructure of the alloy in different states,observing the precipitated phase by transmission electron microscopy(TEM)and testing the hardness and tensile properties of the alloy after heat treatment.The experimental results show that the addition of Sc significantly refines the microstructure of the grains,and the as-cast grains decrease from 100-500μm to about 50μm.The addition of Sc element greatly improves the plasticity of the alloy.After the aging treatment,the elongation after fracture of the alloy increased from 10.82%to 13.60%,but the yield strength reduced from 668 MPa to 657 MPa.By comprehensively calculating the grain size and precipitation phase strengthening,the reasons for the decrease of the yield strength of the peak-aged 7056 aluminum alloy were analyzed in detail.Theoretical calculations show that when 0.2%of Sc is added to the alloy,after peak aging treatment,the strength of the alloy will decrease by 12.005 MPa,which is close to the test value of 11 MPa.Through the research,the best single-stage aging system condition for the 7056 aluminum alloy was found to be 120℃+16 h,and the corresponding peak hardness and strength were 195.2 HV and 714 MPa,respectively.At this time,the main strengthening phase of the alloy was a disk-shaped and short rod-shaped MgZn2 phase,which was about 4 to 6 nm in size,and the alloy also had a spherical Al3Zr phase with a size of about 20 nm.