| Magnesium alloy has high specific strength and light weight.It has great capability to fabricate lightweight engineering components,but its low strength restricts its application.Aging strengthening can effectively improve the mechanical properties of magnesium alloys.The strengthening effect of precipitates can be improved by adjusting the morphology,number density and the size of precipitates.In addition,recent studies have shown that twinning can change the orientation relationship between precipitates and matrix and further improve the strengthening effect of precipitates,but the relevant research work is still few.ZK60 magnesium alloy is one of the most common commercial magnesium alloys that can be age strengthened.Its main strengthening phases are the plate β2’ precipitates on the basal plane and[0001]α rod-like β1’ precipitates.In order to develop and improve the strengthening mechanism suitable for magnesium alloy,ZK60 magnesium alloy was selected as the research object in this study.The orientation relationship between precipitates and matrix was adjusted through coupling aging and rolling deformation process.Combined with VPSC simulation,the influence of the change of precipitates’orientation on the mechanical properties and micro deformation mechanism of ZK60 magnesium alloy was analyzed,and the following main research conclusions were obtained:① Coupling aging treatment and rolling deformation improved the mechanical properties of ZK60 magnesium alloy.The EAR5 sample rolled along ND after peak aging had the best comprehensive mechanical properties,with tensile yield strength of 371 MPa and elongation at break of 15.5%.This was mainly due to the fine grain strengthening and texture strengthening caused by twins,as well as the precipitation strengthening of precipitates with different morphologies and orientations.The tensile yield strength of EAR10 samples rolled along ND was the best,reaching 383 MPa,but the elongation at break was reduced to 11.1%.At this time,the orientation relationship of most of the precipitates was changed,and the aging strengthening effect was further strengthened.② The strengthening effect produced by adjusting the basal plate β2’ precipitates to prismatic plane and prismatic β1’ precipitates to basal plane was called orientation strengthening.It was qualitatively calculated by Orowan equation about the strengthening effect of β1’ and β2’ precipitates on basal slip and cylindrical slip when they were located on basal and prismatic plane respectively.The results shown that,when the rod-shaped precipitate was on the basal and prismatic plane,the strengthening effect of the basal and prismatic slip had little difference;While adjusting the basal plate β2’ precipitates to the prismatic plane,the strengthening effect on basal slip was doubled,and the strengthening effect on prismatic slip was slightly decreased.③Coupling aging treatment and rolling deformation regulated the orientation relationship between precipitates and magnesium matrix.The following two new orientation relationships were found in TEM analysis:[-12-10]β’2//[0001]α,(0002)β’2//(10-10)α[2-1-10]β’2//[01-10]α,(01-16)β’2//(0002)αThe first orientation relationship was consistent with the results predicted by crystallographic calculation.④ VPSC simulation shown that after two precipitates(β1’ and β2’)in ZK60 magnesium alloy changed the orientation relationships,the strengthening effects of basal slip,prismatic slip and pyramidal<c+a>slip were improved to varying degrees.It shown that adjusting the orientation of precipitates was conducive to improve the CRSS of each deformation mechanism.After the orientation of precipitates was completely changed,the strengthening of prismatic slip and {10-12} tensile twins on CRSS was higher than that of basal slip,resulting in the decrease of the relative starting amount of prismatic slip and {10-12} tensile twins and the increase of the relative starting amount of basal slip. |
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