加钛方式与钛含量对A356合金组织和性能的影响

研究了不同钛含量的电解A356合金的组织和力学性能,并与相应钛含量的熔配加钛A356合金进行了比较.结果表明:随着钛含量的增加,二者的晶粒和一次枝晶都明显细化,硅颗粒尺寸、纵横比均有所降低,硅颗粒圆形度有所增加,意味着硅颗粒形状得到改善.但当钛含量大于0.1%时,这种影响变弱.钛含量和加钛方式对合金的屈服强度和抗拉强度影响不大且二者相当,但塑性随着钛含量的增加而增加,当钛含量达到0.1%时,两种合金均具有最佳的塑性和质量系数.对具有相同钛含量的合金,电解加钛A356合金的晶粒和Si颗粒的尺寸小于相应钛含量熔配加钛A356合金,硅颗粒圆形度也优于相应熔配加钛A356合金,电解A356合金的塑性、质量系数均优于相应钛含量的熔配加钛A356合金,但加钛方式对硅颗粒纵横比影响不系统.

Effect of titanium alloying manner and titanium content on microstructure and mechanical properties of A356 alloys

The microstructure and mechanical properties of electrolytic A356 alloys with different titanium contents were investigated and compared with those of A356 alloys alloyed by melting Al-Ti master alloys. The results show that the grain, primary dendrite and Si particles of both kinds of alloys are obviously refined with increasing titanium content. The aspect ratio decreases and the roundness of Si particles increases, which means that the shape of Si is improved. This effect on the microstructure decreases when titanium content exceeds 0.1%. The effects of titanium content and titanium alloying manner on the yield strength and tensile strength of alloys are trifling, but the ductility increases with increasing titanium content. Two kinds of alloys have the optimal elongation and quality index when titanium content approaches 0.1%. For the alloys with the same titanium content, the sizes of grain and Si particles of electrolytic A356 alloys are less than those of A356 alloys alloyed by melting Al-Ti master alloys. The roundness of Si particles, the elongation and quality index of the former are superior to those of the latter. The effect of titanium alloying manner on the aspect ratio is unsystematic.