Al-Si合金变质元素及其交互作用

铸造Al-Si合金具有轻量化、流动性好、气密性好、收缩率小和热膨胀系数低等优点,已成为铸造业中最受重视的结构材料之一。铸造Al-Si合金的力学性能主要取决于组织中的α-Al相、共晶硅、初生硅、金属间化合物、缺陷以及它们的形态、尺寸和分布,其中硅相和富Fe相的形貌、尺寸及分布对合金性能的影响尤为显著。未变质的Al-Si合金中针片状共晶硅和针状β-Fe相严重割裂基体,粗大块状初生硅和针片状共晶硅尖端和棱角部位产生应力集中,导致合金的性能尤其是塑性、强度和耐磨性显著降低。此外,硬脆的粗大初生硅还会加快机加工刀具的磨损,加工后零部件的表面光洁度也较差,无法满足实际生产的需要。快速凝固、电磁搅拌、超声处理、机械振动等特殊工艺技术虽然可以在一定程度上改善铸造铝硅合金的微观组织和性能,但是都需要专门的设备和特殊的条件,使其应用受到限制。变质处理不需要任何特殊设备,只需添加少量变质元素,就可以实现对其中α-Al相、共晶硅、富Fe相、细化初生硅等的有效调控,具有成本低、方法简单、效果显著等特点,已成为改善Al-Si合金组织、提高性能最有效的途径。然而,各变质元素的变质机理及它们之间的交互作用极其复杂,如何充分发挥各变质元素及它们之间积极的交互作用是当前的研究热点。近年来对单一变质元素的变质作用机理和效果的研究进展迅速,先后发现了Na、Sr、Sb、P、Ti、Mn和RE等都对铸造铝硅合金有一定的变质作用,并且对它们的变质时效性以及经济性都有了充分的认识。与此同时,也有许多研究者开始关注多元素的交互变质作用并在Sr-X、P-X、Mn-X、Ti-X等二元交互变质方面取得了重要的成果,使变质技术更加经济、有效和灵活。本文综述了铸造Al-Si合金常用单一变质元素的特点、变质作用机理和局限性,系统归纳了Sr、P、Ti、Mn和RE与其他元素间的交互作用规律,筛选出具有协同变质作用的二元/多元变质元素交互作用对,以期为深入探究二元/多元变质元素交互作用的机理,开发更高效、多样、绿色的复合变质剂及变质处理方法提供参考。

Modifying Elements and Their Interaction in Al-Si Alloy

Casting Al-Si alloy has become one of the most important structural materials in the foundry industry due to its light weight,good fluidity,good gas-tightness,small shrinkage and low thermal expansion coefficient.The mechanical properties of the as-cast Al-Si alloy mainly depend on defects,morphology,size and distribution of the α-Al phase,the eutectic silicon,the prima-ry silicon and the intermetallic compounds,among which the shape,size and distribution of the silicon phases and the Fe-rich phase have prominent influence upon alloy properties.Needle-like eutectic silicon and acicular β-Fe phases severely segregate the matrix in the undeformed Al-Si alloy,meanwhile the tips and corners of coarse bulk primary silicon and needle-like eutectic silicon are prone to stress concentration,which leads to deterioration in the properties of the alloy,especially plasticity,strength and wear resistance.In addition,the wear of machined tools will be aggravated by hard and brittle primary silicon,and the machined parts will also have poor surface finish,which are unsatisfactory for actual production. Although some special techniques such as rapid solidification,electromagnetic stirring,ultrasonic treatment and mechanical vi-bration,etc.can improve the microstructure and properties of cast Al-Si alloy to a certain extent,their applications are limited by the dependence on particular equipment and specific conditions.The modification treatment,with no device requirement,only involving a small amount of modifying elements,can achieve effective regulation of α-Al phase,eutectic silicon,Fe-rich phase and primary sili-con,and thus has become the most effective approach to structure improvement and performance promotion for Al-Si alloy with the characteristics of low cost,simple process and remarkable effect.However,the modification mechanism of various elements and the interactions of them are extremely complicated,and hence have proved to be the research focus in this field. The cognition about single modifying elements’action mechanism has been undergoing rapid progress in recent years,as Na, Sr,Sb,P,Ti,Mn and RE,etc.have been discovered to be moderately effective upon the modification of cast Al-Si alloy,and the re- search over their deterioration,timeliness and cost is exhaustive.Moreover,many researchers have turned to the multi-element modification and have made considerable strides in the study of binary elements interaction such as Sr-X,P-X,Mn-X and Ti-X, endowing the modification technology with greater cost efficiency,effectiveness and diversity. In this paper,the characteristics,mechanisms and limitations of single modifying elements for Al-Si alloy are depicted.The in-teraction rules of Sr,P,Ti,Mn and RE with other elements are systematically summarized.We illuminate some binary or multiple modifying elements which display synergistic modifying effect,and expect to benefit further exploration for the binary/multi-element interaction mechanism and provide reference for developing more efficient,diverse and green composite modifiers and the adapted modification methods.