Study On The Preparation And Properties Of Magnesium Alloy Foam

Magnesium alloy foam is a kind of new lightweight structure-functional materials with a large number of holes distributed in the magnesium alloy matrix.It has the characteristics of small specific gravity,high porosity,shock absorbability and good biocompatibility.Therefore,it has very broad application prospect.However,due to the complex preparation proces’s,poor mechanical properties and corrosion resistance,the development and application of magnesium alloy foams are limited to the laboratory stage and still can not meet industrial requirements.In order to solve this problem,the preparation process of magnesium alloy foam was investigated,and the best process parameters were determined.The structure parameters of foam magnesium alloy were qualitative analyzed by experiment and image processing technology.The effects of Al and Zn elements on the microstructure,mechanical properties and corrosion resistance of magnesium alloy foam were contrast studied.The main results are as follows:(1)Through the change of raw materials and process parameters,the Mg-6A1 alloy foams with the porosity of 30～70%are prepared by powder metallurgy;the average pore in diameter isl.1 mm,and the pore wall thickness is about and 100～300 μm,and the average hole roundness value is 0.75.By optimizing the process parameters,the best parameters for pressing pressure,sintering temperature and sintering time are 200 MPa,600 ℃ and 6 h,respectivly.(2)During the process of compressive testing,the Mg-6Al alloy foams has obvious elastic zone,platform area and dense area.With the increase of porosity,the elastic deformation stage decreases and the yield stress decreases.The stress-strain curves decreases with the increase of porosity.(3)The sintering process of foam Mg is analyzed.First,the carbamide decomposition occurs at 180～200 ℃ and left the pores in the sintered body.Secondly,the initial metallurgical bonding will be formed between the Mg powder particles when the temperature up to 0.4Tm.As the temperature up to 0.5Tm,the Mg powder particles form a sintered neck through diffusion,and the pore diameter channel tends to be flat and smooth.When the temperature rises to 560～620 ℃,the Mg powder particles spacing decrease and form a continuous network structure,the mesopore are disappearance,and the foam Mg pore structure is stable and smooth hole wall.(4)After adding the alloying element Al,the microstructure of the Mg-xAl(x=0,3,6,9,wt%)alloy foams are mainly composed of α-Mg matrix and β-Mg17Al12 phase.With the increase of Al content,the pore wall structure tends to be smooth and the hardness increase,the yield strength and bending strength increase significantly.When the content of Al increased to 9%,the strength of the alloy will be reduced slightly.In addition,the addition of element Al rduces corrosion rate and increases corrosion resistance.(5)With the addition of Zn,the microstructure of Mg-yZn(y=1,2,3,4,wt%)alloy foams are refined,the hole wall structure tends to be uniform,and the hardness of the alloys is increased.Furthermore,the yield strength and bending strength increase first and then decrease with the increase of Zn content.The yield strength and bending strength of the Mg-3Zn alloy foam reach the highest of 18.3 MPa and 16.1 MPa,respectively.When the Zn content reaches 4%,the yield strength and bending strength decrease slightly due to the hard and brittle intermetallic compound MgZn phase.The corrosion resistance of Mg-yZn(y=1,2,3,4,wt%)alloy foams increases first and then decreases with the increase of Zn content,and the Mg-3Zn alloy foam has the best corrosion resistance.(6)The microstructure of the Mg-zAl-Zn(z=3,6,8,9,wt%)alloy foams are mainly composed of α-Mg matrix and β-Mg17Al12 phase.The addition of Al decreases the interstitial holes and the pore wall structure is more denser and uniform,and the hardness of alloy increases.With the increase of Al content,the yield strength and bending strength of the alloy first increase and then decrease,in which the yield strength and bending strength of the foam Mg-8Al-Zn alloy reach the highest of 24.7 MPa and 20.2 MPa,respectively.At the same time,with the increase of Al,the corrosion resistance of the Mg-zAl-Zn(z=3,6,8,9,wt%)alloy foams increases first and then decreases,and the corrosion resistance of the Mg-6Al-Zn alloy foam is the best.