Microstructure And Wear Behavior Of Light Alloys Strengthened By Mg₂Si

Particle reinforced aluminum and magnesium based composite materials are promising structural materials because they possess various advantages such as high specific strength,large specific stiffness,good thermostability and excellent wear resistance.Recently,these materials are extensively investigated as they can be potentially applied in reducing the weight of automobiles and high-speed trains.However,compared with steels,the strength and wear resistance of particle reinforced aluminum and magnesium based composite materials are still not satisfactory,which hinders their further application.For Mg-Si and Al-Mg-Si alloys,intermetallic Mg₂Si can easily form during smelting process.These large dendrite-like and Chinese character-like Mg₂Si particles may cause cracks in the alloy matrix,thus decreasing the strength and ductility of the alloys.To improve the strength and ductility of Mg-Si and Al-Mg-Si alloys,it is imperative to find effective methods to control the morphology and refine the particle size of both primary and eutectic Mg₂Si.With Mg₂Si as the reinforcing particle,Mg₂Si/Mg and Mg₂Si/Al can be regarded as special composite materials.In recent years,the growing process of primary Mg₂Si has been vastly investigated.Through adding modification agent,the size and morphology of primary Mg₂Si can be effectively controlled.But most of the researches are focused on their mechanical property,the effects of the morphology of primary and eutectic Mg₂Si on the wear resistance of the Mg₂Si reinforced composite materials is seldomly investigated.In this work,the microstructural and size evolution of Mg₂Si particles in Mg₂Si/Mg and Mg₂Si/AZ91 magnesium alloys are studied by controlling Si content in the alloys.The morphological influence of Mg₂Si particles on the strength,ductility and wear behavior of the alloy materials is discussed and an optimized Si content is obtained.In our precious work,Mg₂Si particles with various morphologies are obtained by controlling the modifying elements?Sr-Sb,Be,P,et al?.Based on these results,we have analyzed the relationship between the morphology of Mg₂Si particles and the wear-resisting property of semi-solid extruded Mg₂Si/Al alloys.The following are the main conclusions:?1?At loads of 5 and 35 N,with the increase of Si content from 0%to 15%,the wear resistance of Mg₂Si/Mg alloy has increased from 27.35%to 29.3%?Ploughing is the main wearing mechanism of Mg₂Si/Mg alloy.Higher Si content can increase the number of primary Mg₂Si particles which can protect the Mg matrix,thus enhancing the wear resistance of the alloy material.?2?At 5 and 35 N,with the increase of Si content from 0%to 15%,the wear resistance of Mg₂Si/AZ91 alloy has increased from 31.5%to 35.4%?Compared with Mg₂Si/Mg alloy,increasing the Si content in Mg₂Si/AZ91 alloy exhibits a more obvious reinforcing effect in wear-resistance.Mg₂Si/AZ91 alloy shares the same ploughing mechanism with Mg₂Si/Mg alloy.For Mg₂Si/AZ91 alloy,the increase in Si content can decrease the abrasive dust on the wearing surface,which will decrease the wear rate and enhance the wear resistance of alloy.?3?In Mg₂Si/Al alloy,dendrite,octahedron,cube and tetrakaidecahedron structured primary Mg₂Si particles can be obtained by adding different modifying agent such as Be,P and Sr-Sb.Their wear resistance can be ranked as:dendrite<octahedron<cube<tetrakaidekahedron.The difference in wear rate become more obvious with the increase of the load.After modification,the dendrite structured primary Mg₂Si has transformed into refined polygon structured Mg₂Si particles.?4?For cube and octahedron structured Mg₂Si,wear dust tends to form at their sharp corners.In contrast,tetrakaidekahedron structured Mg₂Si possess a near spherical morphology,and wear dust is less likely to form in such surface because of the absence of obvious sharp corners,thus increasing the wear resistance of the alloy materials.This work has provided valuable data about the wear resistance of Mg-Al alloys,which is conducive to the development of high-performance aluminum and magnesium based composite materials.