Effect Of Electropulsing Treatment On Microstructure And Properties Of Mg-Al-Ca-Mn Alloys

The low alloying Mg-Al-Ca-Mn alloy studied in this paper is a kind of magnesium alloy with low cost and excellent performance,which can be extruded at high speed and has remarkable aging hardening effect,so it has broad commercial application prospect.Although the conventional heat treatment can effectively improve the properties of the alloys,there are many problems such as long process cycle,oxidation,overburning,excessive grain growth and so on.Electropulsing treatment（EPT）is a method of rapid temperature rise,high efficiency,energy saving and environmental protection,which can be used to optimize the microstructure and properties of materials,and has been widely concerned in promoting recrystallization,microstructure refinement,solid state phase transformation and other fields.In this paper,the conventional heat treatment and EPT were applied to reveal the microstructure evolution and toughening mechanism of Mg-Al-Ca-Mn alloy in different initial states under electropulsing by means of microstructure characterization and mechanical properties detection.In addition,the effects of high voltage capacitor discharge treatment on the microstructure and mechanical properties of Mg-Al-Ca-Mn alloy were also studied.The main research results of this paper are as follows:（1）The Mg-1.18Al-0.30Ca-0.46Mn（AXM10304）alloys in solid solution state were subjected to EPT,when the parameters are 4 V（180 MA/m²）80 ms,the grains of the alloy were obviously refined and the mechanical properties reached the best.This is mainly because the thermal and athermal effects of EPT promoted recrystallization,and the short high temperature action time limited the grain growth.The Mg-0.4Al-0.30Ca-0.4Mn（AXM040304）alloys in solid solution state were subjected to electropulsing with the same parameter for several times,it was found that multiple EPT could not further promote recrystallization,which was related to the fewer dislocations in the solid solution sample.There is no obvious precipitation phenomenon after EPT at low pressure and high density,indicating that low voltage electropulsing has limited effect on promoting precipitation.（2）The extruded AXM10304 alloys were subjected to EPT,and the optimal solution parameter was 3 V（80 MA/m²）1400 ms.At the same time,electropulsing preserves more vacancies and dislocations,which makes sample nucleates more easily during aging process.After aging treatment for 60 min,Guinier-Preston（GP）zones were precipitated and peak aging occurred in the sample treated by conventional solution teratment,while Al₂Ca phases were precipitated and over-aging occurred in the sample treated by EPT.Compared with conventional solution treatment,the peak aging time of the AXM10304 alloy was shortened by 30 percent by EPT.（3）The extruded AXM040304 alloys were subjected to high density electropulsing for several times,the basal texture strength of the samples increased first and then decreased with the increase of treatment times.The <10（?）3> texture pole gradually shifted from ND to TD.The<10（?）3>texture pole deflection degree of the sample treated by EPT for 5 times reached the maximum,and the texture was symmetrically distributed along the TD axis.（4）The extruded AXM040304 alloys were subjected to high voltage capacitor discharge treatment.Under the action of 4.5 k V voltage,solute atoms were dissolved and GP zones were precipitated in a very short time.The ultimate tensile strength,yield strength and elongation of the sample were 242 MPa,192 MPa and 10.1%,respectively.This is mainly because EPT accelerates the diffusion of elements,promotes the precipitation of GP zones,refines the microstructure and reduces the dislocation density,so the alloy has good strong strength and plasticity.However,the GP zone was relatively dispersed in the sample and the basal plane texture was weakened,which resulted in the yield strength of the sample treated by EPT was lower than that of the sample treated by conventional solution aging.