Room Temperature Twinning Behavior Of Two Typical Magnesium Alloys And Its Effect On Microstructure And Properties

Magnesium alloy is the lightest metal structural material that can be applied;80%of the currently used magnesium alloy is cast magnesium alloy,and cast magnesium alloy has poor uniformity of properties,which limits the wide application of magnesium alloy.The deformation of magnesium alloy can eliminate the defects of casting magnesium alloy while bringing grain refinement effect and significant improvement of mechanical properties,which can effectively broaden the application of magnesium alloy.Wrought magnesium alloy is the future development direction of magnesium alloy.In the plastic deformation process,slip and twinning are two competing deformation mechanisms in magnesium alloys,and these mechanisms can strengthen magnesium alloys effectively.The slip activation in magnesium alloy is related to the temperature.In high-temperature deformation progress,the non-basal slip of magnesium alloy can be activated efficiently.However,the high thermal conductivity of magnesium alloy will make the temperature drops significantly during hot processing,and decrease the slip activation in magnesium alloy,which is easy to cause the cracking and scrap of the billet.The processing temperature of magnesium alloy needs to strictly control,increasing the difficulty of processing.In deformation processing,the twin nucleated is almost not affected by temperature.Twins can nucleate extensively in room temperature defamation process,which can save energy consumption.Twin boundaries as high-angle grain boundaries,can effectively divide the grain,bringing significant grain refinement,while twin boundaries as two-dimensional recrystallization nucleation sites,can effectively promote the recrystallization of magnesium alloy.It can be seen that it is feasible to introduce a large number of twins in magnesium alloys to regulate the organization of magnesium alloys and improve the mechanical properties of magnesium alloys.In this study,ZK60,a commercial high-strength wrought magnesium alloy,and GW 123,a high-strength heat-resistant magnesium alloy of the Mg-Gd-Y series,which has gained much attention of scholars in recent years,these two magnesium alloys were selected in this study.These two typical magnesium alloys were compressed uniaxially at room temperature,and the twinning behavior during plastic deformation and its effect on the microstructure and texture evolution were systematically investigated by EBSD methods.For ZK60 magnesium alloy {10-12}twinning nucleated at a small strain of 0.25%,and when the strain reached 6%,{10-12} twins nucleated and expanded,and at 10%strain the twins started to engulf the matrix and brings a significant basal texture.In room temperature uniaxial compression,the generation of a large number of {10-12} twin boundaries brings significant grain refinement and enhances the mechanical properties of the magnesium alloy.In addition,the grain reorientation brought by twinning also increases the activation of pyramidal Ⅱ<c+a>slip,which provides the basis for the slip-dominated deformation mechanism in large strain deformation.The twinning behavior of ZK60 magnesium alloy also has strain rate sensitivity at room temperature,which is mainly reflected in the area percentage of twins increases with the increase of strain rate.The twinning behavior of GW 123 magnesium alloy is significantly different from that of ZK60 magnesium alloy.In GW 123 magnesium alloy,the addition of rare earth elements reduces the interfacial energy of {11-21} twinning surface,which results in {11-21} higher order twinning in GW123 magnesium alloy.The {11-21}twins in GW 123 magnesium alloy do not undergo significant growth,and the percentage of area covered by {11-21} twins is still less than 36%when the strain reaches 15%.Therefore,the twinning behavior in GW 123 magnesium alloy does not bring about significant grain refinement or significant texture.In addition,because of the large addition of rare earth elements in GW 123 magnesium alloy,the non-basal slip can be activiated significantly,which makes GW 123 magnesium alloy have relatively excellent plasticity during deformation.The twinning behavior of GW 123 magnesium alloy does not exhibit strain rate sensitivity.