热处理对B细化Al-7Si合金中α相形态及硬度的影响

Effects of Heat Treatment on the Morphology of Primary α Phase and Hardness of B-refined Al-7Si Alloy

研究了热处理温度和保温时间对B细化Al-7Si合金中的α相形态与硬度的影响,并确定了最佳热处理工艺。结果表明,在450℃下,随着保温时间由3h延长到12h,初生α相的形态由不规则的树枝晶向均匀的粒状等轴晶、再向蔷薇状组织转变,保温6h时晶粒形态最理想;在300～540℃之间保温8h时,随着温度的升高,初生α相逐渐由发达的树枝晶向蔷薇状枝晶和粒状晶转变;在400℃和450℃时,可得到尺寸较小、分布均匀的粒状初生α相;在450℃以上保温时,初生α相又开始向粗大、无规则形态演变。通过正交试验可知,最佳热处理工艺温度为(540±10)℃,保温6h。

Effects of heat treatment on morphology of primary α phase and hardness of B-refined Al-7Si alloy were investigated to determine the optimized heat treatment rule.The results indicate that primary α phase is converted from irregular dendrite into uniformly distributed equiaxied granular grain and then into rosette structure with holding for from 3 hours to 12 hours at 450℃,in which the ideal grain morphology can be observed with holding for 6 hours.With holding for 8 hours and increasing temperature from 300 to 540℃,primary α phase is evolved from developed dendrite into rosette and granular structure.Granular primary α phase with smaller size and uniform distribution can be observed in the alloy at 400~450℃,however,with holding at more than 450℃,primary α phase is transformed into irregular coarse morphology.The orthogonal analyses shows that the optimized heat treatment parameters are(540±10)℃ for 6 hours.