Effect of Microstructure on Corrosion Resistance of a High-strength Ultralightweight Mg-Li Alloy
Mg-15Li-6Al alloy was prepared by vacuum induction melting and then the alloy was sub-jected to solution treatment plus air cooling or water cooling respectively.The phase constitution and mi-crostructure of the alloys(as-cast,solution treatment plus air cooling or water cooling),were analyzed by means of X-ray diffraction analysis(XRD)and scanning electron microscope(SEM).In addition,the cor-rosion behavior of the three alloys was studied by gravimetric and electrochemical tests.The results show that the three-state alloys are all mainly composed of β-Li with a little of second phase AlLi,and the fractions of secondary AlLi precipitates in the alloys decrease in the following order:as-cast,solution treatment+air cooling and solution treatment+water cooling.The alloy after solution treatment plus wa-ter cooling is almost composed of single β-Li phase.On the contrary,the corrosion resistance of the three alloys follows the sequence:as-cast＜solution treatment+air cooling＜solution treatment+water cool-ing.Relative to the as-cast alloy,the free corrosion potential increases by 480 mV and the corrosion cur-rent density decreases by three orders of magnitude for the alloy solution subjected to solution treatment plus water cooling.The solution treatment makes more Al to dissolve back into β-Li,and subsequent fast cooling strongly suppresses the precipitation of AlLi.Therefore,the number of micro galvanic couple of Al-Li and β-Li decreases,resulting in marked improvement of corrosion resistance.
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