Preparation Of Aluminum Foams By Powder Metallurgy Method Under Variable Pressure

Foamed aluminum has high specific stiffness,sound absorption,heat insulation,electromagnetic insulation,high damping and other characteristics,widely used in construction,automotive,defense industry and other fields.The cellular structure of aluminum foam has an important influence on its mechanical properties and functional properties.It is important to improve the pore size distribution of aluminum foam and control the thickness of bubble wall.In this thesis,the effects of foaming agent pretreatment,alloy element content and ambient pressure on the evolution of cellular structure during the foaming process of aluminum foams prepared by powder densification were studied.The results are as follows:(1)The melting point of the preform is decreased by adding silicon powder,and the wettability of the oxide and aluminum melt is improved by adding proper amount of Mg powder and the stability of the liquid metal foam can be enhanced to prepare the foam aluminum material.The optimum Si addition was determined to be 11.7wt.%.The content of Mg was 0.6 wt.%.(2)The mechanism of the effect of heat oxidation on the hydrogen evolution behavior of TIH2 was studied.The results of DSC,XRD and SEM showed that the surface of TiH2 particles was oxidized at high temperature,and the thermal decomposition endothermic peak increased from 591? to 607?.When the oxidation temperature of foaming agent is 490? and the mass fraction is 1.0 wt.%,a foamed aluminum material with good uniformity of pore structure can be prepared.(3)The effects of processing parameters such as pressing pressure and foaming temperature on the foaming behavior of aluminum foam were studied.The vickers hardness test results show that the vickers hardness on the surface of the preform increases with the increase of pressing pressure,and the vickers hardness difference between the center and the edge decreases.The expansion rate of aluminum foam samples can reach 366%when the preform pressure is 400 MPA and the heating temperature is 710?.(4)The effect of gas pressure in the cavity on the expansion process of aluminum foam was studied.The results show that the expansion rate and the maximum expansion height of aluminum foam decrease with the increase of argon pressure.When the pressure in the foamed cavity increases from 0.1 MPa to 0.5 MPa,the average pore diameter of the foamed aluminum decreases from 9.8 mm to 2.9 mm,and the average thickness of the bubble wall decreases from 168.9?m to 115.1?m.(5)Quasi-static compression tests were carried out on aluminum foams with different pore structures.The results show that the stress-strain curve of the foamed aluminum prepared by powder densification-foaming method has obvious stress-softening stage and fluctuates greatly.When the pore size decreases and homogenizes,the stress-strain curve becomes less fluctuant and the compressive strength increases from 0.84 MPa to 5.28 MPa.