Microstructure and mechanical properties of strontium-modified ADC12 alloy processed by heat treatment

The effects of heat treatment and strontium （SO addition on the microstructure and mechanical properties of ADC12 alloys were investigated, and two-stage solution treatment was introduced. The results indicated that the addition of Sr obviously refined the microstructure of ADC12 alloys. When 0.05 wt% Sr was added into the alloy, the eutectic Si phase was fully modified into fine fibrous structure; a-A1 and fl-A15FeSi phases were best refined; and the eutectic AlzCu phase was modified into block-like AlzCu phase that continuously distributed at the grain boundary. The ultimate tensile strength （UTS） （270.63 MPa） and elongation （3.19%） were increased by 51.2% and 73.4% respectively compared with unmodified alloys. After the two-stage solution treatment （500 ~C, 6 h＋520 ~C, 4 h）, for 0.05 wt% Sr modified ADC12 alloys, the Si phases transformed into fine particle structure and AlzCu phases were fully dissolved. The peak hardness value of the alloys processed by the two-stage solution treatment was increased by 8.3% and 6.8% respectively compared to solution treatment at 500 ~C and 520 ~C. After the aging treatment （175 ~C, 7 h）, the hardness and UTS were increased by 38.73% and 13.96% respectively when compared with the unmodified alloy.

本文研究了锶(Sr)变质、单级及二级固溶处理以及时效处理对ADC12合金显微组织及力学性能的影响。结果表明,Sr的添加可以显著改善ADC12合金的显微组织。当Sr添加量为0.05 wt%时,共晶硅相完全转变为细小纤维状,α-Al相和β-Al_5FeSi相得到了较佳的细化效果,同时Al_2Cu相转变为块状,并连续分布在晶界处;其极限抗拉强度(270.63 MPa)和伸长率(3.19%)较基体合金分别提高了51.2%和73.4%。经二级固溶处理(500°C,6 h+520°C,4 h)后,共晶硅相转变为细小颗粒状,Al_2Cu相完全溶解;其峰值硬度较500°C和520°C下单级固溶处理分别提高了8.3%和6.8%。时效处理(175°C,7 h)后,其硬度和极限抗拉强度较基体合金分别提高了38.73%和13.96%。