Study On Near Interface Microstructure And Mechanical Properties Of Mg / Mg Layered Composites

Magnesium alloys have great potential for applications in aerospace and transportation with low density and high specific strength.However,the disadvantages such as poor plasticity and thermal stability hinder the mass application of magnesium alloys.It is found that the addition of rare earth elements can substantially improve the strength,plasticity and thermal stability,but increases the cost of magnesium alloys.Recent researches have shown that the introduction of structures such as layers and gradients can further improve the strength based on the base element material while obtaining better plasticity.In this paper,the laminate composites prepared by hot-rolling method using commercial magnesium alloy(AZ)and rare-earth magnesium alloy(Mg-Y)as raw materials.the microstructure near the interface and mechanical properties were studied,which provide theoretical guidance for the development of magnesium alloy with high strength and toughness,high thermal stability and low rare-earth content.AZ31/Mg-1Y/AZ31 composites with good interfacial bonding can be successfully prepared by applying 40% reduction at 400°C temperature.The microstructure and chemical composition distribution of the materials were characterized by scanning electron microscopy(SEM),energy spectrometry(EDS)and electron backscatter diffractometry(EBSD).The results showed that,the grain size in the near-interface region was finer than that in the central region in the Mg-1Y layer of the AZ31/Mg-1Y/AZ31 composite,while finer Al-Y phase particles were formed than in the conventional cast Mg-Al-Y alloy.In order to determine the mechanism of microstructure formation in the near-interface region,additional hot rolling and diffusion annealing were performed on the basis of AZ31/Mg-1Y/AZ31 composites.The analytical results indicate that the formation of the near-interface fine grain region is closely related to the precipitation of Al-Y phase particles.In addition,the near-interface region of the Mg-1Y layer were strengthened by the grain refinement and the formation of Al-Y phase particles.In order to further explore the method of regulating the second phase particles near the interface,the preparation of Mg/Mg composites under different diffusion annealing processes and different alloy content raw material sheet conditions was carried out.The results shown that the interfacial reaction second phase particle distribution widens with increasing diffusion annealing temperature/time.The alloy content in the raw material sheet has a significant effect on the type and morphology of the second phase at the near interface of the composite,and only when Al/Y ? 3(mass ratio),the diffusely distributed Al-Y phase particles appear in the near interface region,and the larger the Al/Y ratio,the more the content of the diffusely distributed second phase.The results of this paper show that fine,diffusely distributed high melting point particles can be prepared in magnesium alloys by solid-state diffusion reaction,which provides a new method for preparing high-strength and high-temperature stable magnesium alloys.