P-Cr-Ti复合变质Al-25%Si合金时Cr-Ti作用机理

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。

The Action Mechanism of Cr-Ti in Al-25%Si Alloy Modified by P-Cr-Ti

Compound modification of Al-25% Si alloy with P-Cr-Ti is utilized to study the change of the solidification microstructure and the effect mechanism of Cr and Ti elements. The results indicate that primary Si in the solidification microstructure decreases by 12.24%~51.65% in the Al-25% Si alloy modified by the compound modifier P-Cr-Ti compared with simple phosphorus modification, and the distribution of the primary Si is more uniform. The Cr and Ti elements in the Al-25%Si alloy mainly appear as compounds including TiAl₃, Ti₇Al₅Si₁₂, Al₇Cr and Al₁₃Cr₄Si₄, while a minor amount of P exists in the compounds containing Ti. Compounds containing Ti appear as long strips. Compounds containing Cr, which distribute among the primary Si, appear as granular or short rods. The number of the compounds containing Cr and Ti is increased with the increase of the cooling rate. The TiAl₃ phase initiated by Al-6.5%Ti alloy wanders in the melt during the modifier process. The {110} crystal of TiAl₃ phase becomes the nucleation basal of the Si phase, causing the primary Si to precipitate continuously and to refine the primary Si with a limited refining ability. Compounds containing Cr formed among the primary Si prevent the growth and gather of the primary Si during the solidification, which leads to the distribution of the primary Si more even.