Mg_2Si/Al内生颗粒增强复合材料的研究进展

Progress of the Mg_2Si/Al in Situ Particle Reinforced Composite

根据铝与Mg_2Si的共晶反应而制备的Mg_2Si/Al内生颗粒增强复合材料具有密度小、热稳定性高、增强体分布均匀、切削加工性和成型性能良好等优点,受到了国内外的广泛关注。这一材料的关键问题在于其中的Mg_2Si相为小晶面长大模式,尺寸粗大、形貌规则,导致复合材料脆性严重,通常情况下其伸长率不足1.5%。本文对这一材料的变质处理、材料体系、成型与制备技术三方面进行了综述。Mg_2Si的变质与细化研究是这一领域最为活跃的方面,研究证明,几乎所有在铝合金中具有变质作用的元素对Mg_2Si都有一定的变质作用,其中变质作用最为显著的是稀土元素、碱金属和碱土金属以及B、Sb、Ti、Mn、Ni等微合金化元素。Al/Mg_2Si的形貌通过恰当的变质处理,铸态Mg_2Si/Al内生颗粒增强复合材料的强度可以达到280MPa,伸长率可以达到约4%,显著高于基体材料的铸造性能。材料体系的选择方面的研究比较薄弱,主要集中在铝镁硅合金系,Mg_2Si含量以15%的近共晶成分为多,过共晶体系中Mg_2Si含量最高也没有超过30%。材料成型与改性方面的研究也只是刚刚开始,这一材料无一例外都是凝固成型。研究发现,凝固前的熔体过热处理和搅拌等熔体预处理都可以改善Mg_2Si的形貌和尺寸,粗大的初生Mg_2Si的平均尺寸可以细化到约40μm;低过热浇注及凝固过程加压和快冷可以显著改善Mg_2Si的尺寸和形貌,在快速凝固条件下,Mg_2Si将由小晶面长大模式转变为非小晶面连续长大模式;凝固后的热变形以及热处理也能显著改善其微观组织和性能。内生Mg_2Si/Al复合材料的成型技术研究比较薄弱,其中,挤压铸造Mg_2Si/Al复合材料具有突出的优势,挤压铸造的A380铝合金-Mg_2Si复合材料,平均尺寸由75μm降为30μm,形状系数由0.77降为0.22。

Based on the eutectic reaction of aluminum and Mg2Si,the Mg2Si/Al in situ particle reinforced composite has been prepared by a solidification technology.Because of having low density and the advantages of high thermal stability,uniform distribution of reinforcement,satisfied cutting machinability and good formability,the composite materials have been widely concerned at home and abroad,and it is expected to have great market potential.However,the properties of the Mg2Si phase is very brittle,the elongation of the composite is less than 1.5% under normal preparing conditions.In this paper,the researches on modification of the material,material performance characters and preparation techniques are systematically introduced and reviewed.The study on modification and refinement of Mg2Si is one of the most active aspects.It has been proved that all of the modifying elements used in traditional aluminum alloys have some effects on the morphology and size of the Mg2Si in the composites.Among them,the most significant modifying elements are the rare earth elements,alkali metals and alkaline earth metals and some micro-alloying elements such as B,Sb,Ti,Mn,Ni.After the modification treatments,the strength of the cast Mg2Si/Al in situ particle reinforced composite can reach to 280 MPa,and their elongation can reach about 4%,which is significantly higher than the matrix material.It is presented that the selection of materials system is relatively weak.The matrix material of the composite is mainly of the aluminum-magnesiumsilicon alloy system,and the Mg2Si content is of 15%of the near eutectic composition in most cases,not seen more than 30%of the highest content.The researches of the material process and their effects is only just beginning.The processing technology of the material,without exception,is the solidification forming.Fortunately,it has been found that melt pretreatment,such as melt superheat treatment and stirring before solidification,can significantly improve the morphology and size of Mg2Si.Moreover,the size and shape of Mg2Si can be significantly improved by low superheat pouring,high-pressure solidification and fast cooling.Under the condition of rapid solidification,the microstructure and properties of the Mg2Si can be significantly improved by the transformation of the small faceted growth mode into the continuous growth mode.The hot deformation such as hot extrusion,hot forge and hot rolling are proved be the useful processing technology.The research on the forming technology is relatively weak,among which,squeeze casting has prominent advantages.The average size of the squeeze casted A380Al-Mg2Si composite decreased from 75μm to 30μm,and the shape coefficient decreased from 0.77 to 0.22.