原位TiC颗粒含量对近液相线铸造7075铝合金二次加热组织的影响

Effect of in-situ TiC concentration on reheating microstructure of near-liquidus cast 7075 A1 alloy

采用原位反应近液相线铸造法制备具有不同原位TiC颗粒含量的TiCp/7075铝基复合材料,在7075铝合金固?液两相区间(477～635℃)的580和600℃进行二次加热并保温20min,水淬固定其半固态组织,应用Image Pro Plus软件测量平均晶粒尺寸及形状因子,研究原位TiC颗粒含量对该合金二次加热组织的影响。结果表明:当原位TiC颗粒质量分数为0～4.4%时,随着原位TiC颗粒质量分数增加,合金铸态组织直接转变为等轴晶组织,且在二次加热过程中,原位TiC颗粒对晶粒的长大行为具有明显的抑制作用;在相同的二次加热条件下,4.4%TiCp/7075铝基复合材料的平均晶粒尺寸比7075基体合金的减少30～40μm,更加适合于半固态触变成形。

The TiCp/7075 Al matrix composites with different TiC particles contents were prepared by in-situ reactive near-liquidus casting, the sectioned specimens were reheated isothermally at 580 and 600℃ for 20 min in the two-phase （liquid＋solid） region （477-635℃） of the near-liquidus casting 7075 alloy, then quenched in water. The grain size was measured by Image Pro Plus and the effect of in-situ TiCparticles on the reheating structure was analyzed. The result shows that when the content of TiC particles is 0-4.4% （mass fraction）, the in-situ TiC particles can not only keep near-liquidus casting 7075 alloy with finer and globular microstructure, but also control the grain growth evidently during reheating under the same condition. The average grain size of 4.4%TiCp/7075 Al matrix composites is 30-40μm less than that of 7075 alloy, therefore it is more suitable for thixoforming.