Si含量和热处理制度对铸造Al-Si合金组织和性能的影响

为提高铸造Al-Si合金的力学性能,研究了Si含量和热处理制度对Al-Si合金组织和性能的影响。结果表明,Si含量、固溶冷却介质、固溶温度、时效时间、时效温度对Al-Si合金硬度的影响依次减小。Al-Si合金的最优Si含量及热处理制度为Si含量12%,480 ℃固溶120 min,盐溶液冷却及175 ℃时效90 min。随着Si含量的增加,Al-Si合金硬度和抗拉强度提升;但当Si含量超过共晶点时,方块状初生硅相析出,易形成应力集中使得合金强度降低,断裂方式由韧性断裂变为解理断裂。铸态Al-Si合金中共晶硅为长针状,经最优工艺热处理后,长针状转变为短棒或颗粒状,共晶硅更加分散,在拉伸过程中应力集中减少,位错运动阻力增加,使得Al-Si 合金的力学性能提高。

Effect of Si content and heat treatment on microstructure and properties of as-cast Al-Si alloy

In order to improve its mechanical properties, the effect of Si content and heat treatment on the microstructure and properties of the as-cast Al-Si alloy was studied systematically. The results show that the effect of Si content, cooling medium, solution treatment temperature, aging time and aging temperature on the hardness of the alloy decreases in turn. The optimal Si content and the optimal heat treatment process are 12% Si and solid solution treating at 480 ℃ for 120 min+salt bath cooling+aging at 175 ℃ for 90 min, respectively. With the increase of Si content, the hardness and tensile strength of the alloy increase; but when the Si content is too high, the precipitation of block-shaped primary silicon tends to form stress concentration then reduces the strength of the alloy, and the fracture mode changes from ductile fracture to cleavage fracture. The eutectic silicon in as-cast Al-Si alloy is long needle like. After using the optimal heat treatment, the long needle-like silicon transforms into short rod or granular shape, and the eutectic silicon is more dispersed, the stress concentration decreases during tension, and the dislocation movement resistance increases, all of which improve the mechanical properties of the Al-Si alloy.