Preparations And Compressive Properties Of Mg-Zn-Y And MAO/Mg-Zn-Y Foams

Metal foams have attracted considerable researchers’attention in the past several decades.Metal foams are widely used in rail transit,aerospace and medical devices due to the combination of various excellent properties,i.e.low weight,good damping performance and excellent energy absorption characteristics.In engineering applications,with the demand for lightweight engineering components,low-density Mg foams have become the potential candidate.However,the relatively low mechanical properties of Mg foams cannot meet the service requirements of engineering applications and urgently need to be resolved.Therefore,in order to improve the compressive properties of Mg foams,rare earth alloying technology and micro-arc oxidation surface treatment technology are adopted to adjust the composition and structure of Mg foams,and generate ceramic coating on their inner and outer surfaces.In this paper,open-cell Mg-2Zn-x Y（x=0.4,3 and 6 wt.%）foams with different rare earth element yttrium（Y）addition were prepared by the pressure infiltration route.The effects of Y addition on the microstructure,compressive properties of as-prepared Mg-Zn-Y foams were studied,and the corresponding failure behavior of the Mg-Zn-Y foams was investigated.In addition,MAO/Mg-Zn-Y composite foams were prepared by micro-arc oxidation（MAO）treatment of above Mg-Zn-Y foams.The effect of Y content on the microstructure and compressive properties of the composite foams were studied,and the failure behavior of these foams were also analyzed.The main results are as follows:1.Increasing Y addition has a significant effect on the microstructure of Mg-Zn-Y foams.The microstructures of the Mg-Zn-Y foams are refined with increasing Y content.Increasing Y addition promotes the formation of the second phase.As a result,the Mg-2Zn-0.4Y foam consists ofα-Mg,MgZn₂ phase and a few I phase（Mg₃Zn₆Y）.The Mg-2Zn-3Y foam is composed ofα-Mg and continuous W phase（Mg₃Zn₃Y₂）at the grain boundaries.The Mg-2Zn-6Y foam is mainly composed ofα-Mg and LPSO phase(Mg₁₂Zn Y),which also locates at the grain boundaries.2.Increasing Y addition and test temperature have significant effects on the compressive properties of Mg-Zn-Y foams.At the same temperature,the compressive strength and energy absorption capacity of Mg-Zn-Y foams increase with increasing Y content.When the Y content is constant,the compressive strength and energy absorption capacity of Mg-Zn-Y foams decrease with increasing testing temperature.Moreover,Y content and temperature have no significant effect on the average energy absorption efficiency of the Mg-Zn-Y foams.3.Increasing Y addition has no significant effect on the microstructures of the ceramic coatings on the MAO/Mg-Zn-Y composite foams.The MAO coatings on composite foams exhibit similar surface morphology,including porosity and cross-sectional thickness.The MAO coatings of composite foams with different Y content are both composed of MgO phase and Mg Al₂O₄ phase.In addition,the MAO coatings can be divided into dense layer and loose layer from the inside to the outside.4.The Y content and temperature have significate effects on the mechanical properties of MAO/Mg-Zn-Y composite foams.At the same temperature,the compressive strength and energy absorption capacity of composite foams are improved with the increasing Y content.When the Y content is constant,the compressive strength and energy absorption capacity are decreased as the temperature increases.In addition,Y content and temperature have no significant effect on the average energy absorption efficiency of the composite foams.The compressive strength and energy absorption capacity of the Mg-Zn-Y foams are enhanced after micro-arc oxidation.5.The failure behavior of MAO/Mg-Zn-Y composite foams at room temperature is mainly brittle fracture.The plasticity of the composite foam struts increases with increasing test temperature.The loose layer of the MAO coating cracks and falls off during the compression process,and the dense layer undergoes transcrystalline fracture.