铸态铝镁钪合金的热塑性

Thermoplastic of Al-Mg-Sc casted alloy

采用半连续铸锭冶金法制备一种成分为Al-6Mg-0.4(Sc+Zr)的合金,铸锭样品经均匀化退火后,测试其在250,300,350,400,450,475和500℃时的瞬时拉伸力学性能,借助扫描电镜(SEM)和透射电镜(TEM)的观察和分析,研究该合金的高温变形及断裂行为。结果表明:合金抗拉强度和屈服强度随温度的升高而降低,而其伸长率随温度的升高而增大;合金在300℃以下拉伸,断口为穿晶断裂型;在300℃以上拉伸,断口由穿晶断裂逐步向沿晶断裂转变;在400℃以上拉伸,断口基本上是沿晶断裂。在400℃以上变形,晶界区域有大量的强滑移带;在400℃以上晶内强度高于晶界强度,拉伸时变形优先在晶界区域发生,变形不均匀的结果导致铸坯热加工过程中开裂。Al-6Mg-0.4(Sc+Zr)合金铸坯的最佳热加工温度范围为350～400℃,在此条件下,合金的变形抗力较低,热塑性较好,又不出现热裂纹。

An Al-6Mg-0.4（Sc＋Zr） alloy was prepared by semicontinuous ingot metallurgy method. In order to determine the best thermal process technics, the thermoplastic of Al-6Mg casted alloy was studied. The tensile properties of the casted sample were tested at 250, 300, 350, 400, 450, 475 and 500℃, respectively, after homogenizing annealing treatment. The high temperature deformation and fracture behavior of the alloy was investigated by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results show that its tensile strength and yield strength decrease, while the elongation increases with the increase of temperature. The results of SEM fracture analysis show that the tensile fracture is transgranular below 300℃, the morphology changes gradually from transgranular fracture to a fracture appearance with the intergranular, and the fracture is intergranular above 400℃. TEM results also indicate that after deforming above 400 ℃, a large number of slip bands occur in grain boundary region. Over 400 ℃,the strength of the crystal is higher than that of the grain boundary and tensile deformation occurs firstly in the grain boundary region. Inhomogeneous deformation leads to casting thermal processing cracking. The best thermal processing temperature of A1-Mg-Sc casting alloy is between 350-400℃. Under these conditions, the deformation resistance of the alloy is lower and thermoplastic is better, so thermal crack will not arise.