Preparation And Compressive Properties Of High Performance Magnesium Foams

As a new type of structural and functional material,the porous magnesium foams possess a good combination of low density,high specific strength and specific stiffness.Moreover,they also exhibit good energy absorption capacity,noise reduction,damping properties and biocompatibility.Therefore,they have potential application background in the field of aerospace,automotive,national defense and military,medical and construction.However,due to magnesium matrix exhibits relatively low strength and poor high-temperature mechanical properties,the mechanical properties of magnesium foams need to be improved.In order to overcome these problems,the surface treatment technology and the addition of rare earth?RE?elements are carried out to design and fabricate high performance magnesium-based foams.And the approaches have important significance for the basic theory and practical applications of magnesium foams.In this paper,open-cell AZ91D magnesium alloy foams were prepared by infiltration casting method,and the effects of porosity and temperature on the compressive properties of AZ91D magnesium alloy foams were studied.The MAO-EN composite coating was prepared by surface treatment to reinforce AZ91D magnesium alloy foams.The effects of composite coating on the compressive properties of the magnesium foams were primary investigated.In addition,open-cell Mg-xGd-2Zn?x=4,6,8 wt.%?alloy foams were fabricated by rare earth alloying method.The effects of Gd contents on the compressive properties and energy absorption capacity at different temperature were explored,the compression deformation behavior was analyzed and the failure mechanism was discussed preliminarily.The main results of this study are as follows:1.Porosity and temperature had great influence on the compressive strength and energy absorption capacity of the open-cell AZ91D magnesium alloy foams,but they showed negligible effects on the energy absorption efficiency.As the increase of temperature,the failure mode of the pores of AZ91D magnesium foams mainly changed from fracture?tearing?to bending?buckling?,and the fracture of foam strut varied from brittle fracture to ductile fracture.2.The composite coating at the inside and outside surfaces of the open-cell AZ91D magnesium foams was obtained by micro-arc oxidation?MAO?and electroless plating?EN?.It was showed that the MAO and Ni-P coatings exhibited"crater"and cellular structure respectively.The MAO coatings bonded well with AZ91D matrix.The Ni-P coating interacted with MAO coating excellently,which improved the bonding force.3.MAO-EN composite coating can significantly improve the compressive strength and energy absorption capacity of AZ91D magnesium foam at room temperature.However,the compressive strength and energy absorption capacity gradually decreased with the increase of compressive temperature,and the effects of the temperature on the energy absorption efficiency were not obvious.The failure mode at room temperature was mainly fracture of the foam strut,including the rupture of coating and the stripping between MAO and EN coating.And the shedding of Ni-P coating decreased significantly with the increase of the temperature.4.With the increase of Gd contents,the microstructure of Mg-x Gd-2Zn?x=4,6,8 wt.%? magnesium foams was refined.And the second phase volume fraction increased as well.The formation of a long-period stacking ordered structure?LPSO?phase was promoted by the increase of Gd contents.The second phase of Mg-4Gd-2Zn alloy foams was only?Mg,Zn?₃Gd phase,while the second phase of Mg-6Gd-2Zn and Mg-8Gd-2Zn alloy foams were?Mg,Zn?₃Gd phase and LPSO phase,respectively.5.With the increase of Gd contents,the compressive strength and energy absorption capacity of Mg-xGd-2Zn?x=4,6,8 wt.%?foams were constantly improved.But the energy absorption efficiency did not change significantly.With the increase of compression temperature,the compressive strength and energy absorption capacity of Mg-Gd-Zn alloy foam decreased obviously,but the effect on energy absorption efficiency was not obvious.