Effects Of Hydrogen Removal On Microstructures And Mechanical Properties Of Magnesium Alloys Melt

Magnesium alloys are the lightest structural materials.It has great prospect on automobile,electro-communication,aviation,and military industry,etc.However,there are many basic and technological problems required to be solved for further application of magnesium alloys.Thereinto,the specific effects of gas capturing on properties of magnesium alloys are still not clear,although magnesium alloys always absorb large quantity of gas.This work subjected pure magnesium,several binary magnesium alloys and industrial magnesium alloys to investigate the hydrogen behaviors in different magnesium alloys applying different refining process.Meanwhile,their corresponding effects and mechanism on degassing,microstructures and mechanical properties were also studied.The obtained results were summarized as follows:(1)Hydrogen stays in different magnesium alloys with various manner and quantity.Ca and RE elements(Y,Gd)could strongly increase the hydrogen content in magnesium alloys,while Al and Zn have limited impact on the hydrogen content in magnesium alloys.Hydrogen is mainly solid soluted in the matrix,for Mg-Al,Mg-Zn and Mg-Ca based alloys,but there are hydrides in Mg-Y and Mg-RE alloys.Hydrogen contents has no obvious effect on microstructure of alloys,but significant effects on elongation and corrosion resistance.(2)Purging argon bubbles are efficient degassing method for pure magnesium and AZ91 alloy melt,and appropriate flow(1.0L/min)has the highest degassing rate(60%and 42%,respectively).Multi-step purging argon is more efficient than single step ones,in the same frame of treating time.The macrostructures pure magnesium were not changed after argon treatment,but the tensile strength and the elongation was enlarged strongly.(3)Hydrogen removal in AZ91-Ca alloy melt can be successfully achieved by argon,ultrasound and the recombination of the two,but degassing efficient varied much for the three methods.The degassing rate changed deeply with the flow of argon and treatment time.With the effect of high power ultrasonic,the smaller flow of argon can reach the higher degassing rate.Hydrogen content of AZ91-Ca magnesium alloy melt after the ultrasound-argon recombination treatment droped to 12?15?g/g,and the degassing rate is 40%.The amount of shrinkage porosities and microporosities decrease sharply after degassing treatment.The recombination treatment of ultrasound-argon can disperse the second phases.The second phases along grain boundary were much refined after treatment,so the tensile strength and elongation increased obviously.(4)The water simulation experiment of ultrasound-argon recombination treatment indicated that the recombination treatment could increase the depth and dispersion of argon bubbles into the liquid.It also suggested that the specific surface of argon bubbles increased and the time stayed in liquid was prolonged.Thus,the recombination of ultrasound-argon can remove hydrogen from magnesium melt efficiently.