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采用P-Cr-Ti复合变质处理Al-25%Si(质量分数)合金,重点研究了凝固组织的变化以及Cr、Ti元素的作用机理。结果表明:与单一的P变质相比,经P-Cr-Ti复合变质后,Al-25%Si合金凝固组织中初生Si的尺寸减小了12.2%~51.7%,并且初生Si分布的均匀程度增加。Al-25%Si合金中Cr、Ti主要以TiAl_3、Ti_7Al_5Si_(12)、Al_7Cr、Al_(13)Cr_4Si_4化合物的形式存在,同时有少量的P分布在含Ti化合物中。含Ti化合物呈长条状、短杆状;含Cr化合物呈菊花状、网状,分布在初生Si之间。含Cr、Ti化合物的数量随冷却速度的增加而增加。变质处理时Al-6.5%Ti合金带入的TiAl_3相,具有使初生Si持续析出和细化初生Si的作用,但细化能力有限。凝固过程中初生Si周围形成的含Cr化合物和αCr阻止初生Si的长大与聚集,促使增加初生Si分布均匀程度。
Al-25% Si (mass fraction) alloy was treated by P-Cr-Ti composite modification, and the change of solidification structure and the action mechanism of Cr and Ti elements were mainly studied. The results show that compared with a single P metamorphism, the size of primary Si decreases by 12.2% -51.7% after P-Cr-Ti composite metamorphism, and the homogeneity of primary Si distribution increase. In Al-25% Si alloy, Cr and Ti are mainly in the form of TiAl_3, Ti_7Al_5Si_ (12), Al_7Cr and Al_ (13) Cr_4Si_4 compounds with a small amount of P distributed in Ti-containing compounds. Ti-containing compounds were elongated, short rod-like; Cr-containing compounds were daisy-like, reticular distribution between primary Si. The amount of Cr-containing and Ti-containing compounds increases with the cooling rate. The Al-6.5% Ti alloy brought into the TiAl_3 phase during metamorphism treatment has the effect of continuously precipitating and refining primary Si, but its refining ability is limited. The Cr-containing compounds and αCr formed around primary Si during solidification prevent the growth and aggregation of primary Si and promote an even distribution of primary Si.