等温热处理对B细化Al-7Si合金α相形态及性能的影响

Effects of Isothermal Heat Treatment on Morphology of Primary α Phase and Properties 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℃,当保温时间由3 h延长到12 h,初生α相的形态由不规则的枝晶向均匀的粒状等轴晶再向蔷薇状组织转变,保温6 h时晶粒形态最理想;在300～540℃保温8 h时,随温度的升高,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,最佳热处理工艺是(540±10)℃×6 h。

The effects of isothermal heat treatment on morphology of primary α and hardness of B-refined Al-7Si alloy were investigated. In addition, the optimum heat treatment procedure was also determined. The results show that, at 450℃ with different holding time from 3 h to 12 h, morphology of primary α phase is converted from irregular dendrite to granular homogeneous equiaxed grains then to rosette structure. The primary α phase is gradually converted from dendrite into the rosette dendrite and then into particle crystal with increasing of temperature by holding 8 h at 300-540 ℃. Fine and uniform distributed particle α phase can be obtained at 400 ℃ or 450 ℃. However, the primary α phase has changed into large and irregular shape when the temperature increase to 450 ℃. The orthogonal analysis shows that the optimum heat treatment process is （540±10）℃ for 6 h.