Researching On Impact Deformation Behavior Of Magnesium-Lithium Alloys

Four different magnesium alloys, Mg-8%Li alloy (two-phase alloy), Mg-3.5%Li (single-phase alloy) and Mg-Li-RE alloys (Mg-Li-Y, Mg-Li-Nd) were processed. The dynamic stress-strain behavior of four different magnesium alloys were investigated and the localized deformation behavior of Mg-8%Li alloy were discussed. The dynamic impact compression experiments were carried out on Mg-8% Li alloy by using different length projectiles(100mm, 200mm, 300mm)while the Mg-3.5%Li alloy and Mg-Li-RE alloys used 200mm length projectile.The main results are as follows.(1)The dynamic impact compression experiments for the Mg-8%Li alloy were carried out using the Hopkinson pressure bar.The dynamic stress-strain curves were gained.The strain-rate effect and the condition of the localized deformation were analyzed.The results showed that Mg-8%Li alloy dynamic stress-strain curve increased (strain rate positive effect) at first and then decreased (strain rate negative effect) with the strain rate increasing,that is,the behavior of stress-strain of Mg-8%Li alloy transformed the positive effect of strain rate to the negative effect of strain rate.The turning point of the strain rate effect had closely relation with the phenomenon of the localized deformation. The strain of this alloy that the localized deformation needed decreased (0.32→0.28→0.185) with the increasing strain rate (2750/s→3700/s→4600/s). This indicated that the Mg-8%Li alloy must get the corresponding strain at certain strain rate to form deformation band.But when the strain-rate increased to some certain degree, distortion will restrain the localized deformation. Localized deformation and the damnification caused by the tiny crack both took some action to the negative strain-rate effect.(2)The dynamic impact compression experiments for the Mg-Li alloy and Mg-Li-RE (RE:Y,Nd) alloys were carried out using the Hopkinson pressure bar.The dynamic stress-strain behavior and strain rate effect of the three alloys were analyzed. Mg-3.5%Li alloy showed the doubt characteristics as the positive and negative strain-rate effects. After the addition of rare-earth elements Y,Nd, the strengths of Mg-Li-RE (RE:Y,Nd) alloys were improved while the brittleness enhanced. The dynamic stress-strain curves of Mg-Li-Y alloy and Mg-Li-Nd alloy decreased with the strain rate increasing and showed the negative strain-rate effect. The damnification caused by the tiny crack took some action to the negative strain-rate effect.