深冷处理对AZ31镁合金TIG焊接接头组织和性能的影响中期报告

深冷处理对AZ31镁合金TIG焊接接头组织和性能的影响中期报告摘要：本文研究了不同深冷处理（-60℃、-80℃、-100℃）对AZ31镁合金TIG焊接接头组织和性能的影响。研究结果表明，随着深冷处理温度的降低，接头强度和延展率先升高后降低。最佳深冷处理温度为-80℃时，接头拉伸强度和延展率分别为222.5MPa和10.2%，远高于未经深冷处理的接头。同时，深冷处理可以有效减少接头的气孔和裂纹，提高接头的成形性和可焊性。关键词：AZ31镁合金；TIG焊接；深冷处理；组织和性能Introduction:AZ31magnesiumalloyhasbeenwidelyusedinaerospace,automotiveandotherfieldsduetoitshighstrength-to-weightratio,goodductilityandexcellentcorrosionresistance.However,thelowmeltingpointandhighthermalconductivityofmagnesiumalloymakeitdifficulttoweld.Tungsteninertgas(TIG)weldingisacommonmethodforweldingmagnesiumalloy,butitsmechanicalpropertiesandweldabilityareaffectedbythemicrostructureoftheweldzone.Deepcryogenictreatmentisanewtechnologythatcanimprovethemechanicalpropertiesofmaterialsbyfreezingthemtoaverylowtemperature(-100℃to-196℃)andthenslowlywarmingthemup.Thistreatmentcanimprovethestrength,toughness,wearresistanceandelectricalconductivityofmaterials,andhasbeenwidelyusedinthefieldofmaterialsengineering.Inthisstudy,weinvestigatedtheeffectofdifferentdeepcryogenictreatments(-60℃,-80℃and-100℃)onthemicrostructureandmechanicalpropertiesofAZ31magnesiumalloyTIGweldedjoints.Materialsandmethods:AZ31magnesiumalloyplateswithathicknessof2mmwereusedasweldingmaterials.ThechemicalcompositionofthematerialisshowninTable1.Table1ChemicalcompositionofAZ31magnesiumalloyMaterialMgZnAlMnSiFeCuNiOthersAZ31Bal.2.5-3.50.6-1.40.2-1.00.050.0050.050.0050.3TIGweldingwascarriedoutonaGYRD-315Aweldingmachine,usingapuretungstenelectrodewithadiameterof2mm,anargongasflowrateof10L/minandaweldingcurrentof60A.Theweldingspeedwas50mm/minandtheweldinganglewas70°.Threedifferentdeepcryogenictreatments(-60℃,-80℃and-100℃)wereperformedontheweldedjointsfor1h,andthenthespecimenswereallowedtowarmuptoroomtemperaturenaturally.Resultsanddiscussion:Microstructureanalysis:Themicrostructureoftheweldedjointswasobservedusinganopticalmicroscopeandascanningelectronmicroscope(SEM).Theresultsshowedthatthemicrostructureoftheweldedjointsconsistedofcolumnarcrystalsandequiaxedcrystals.Withthedecreaseofdeepcryogenictreatmenttemperature,thedendritesoftheweldzonebecamefinerandmoreuniform,andtheweldingdefectssuchasshrinkageporosityandcracksweresignificantlyreduced.Mechanicalproperties:Themechanicalpropertiesoftheweldedjointswereevaluatedbytensiletesting.Theresultsshowedthatthetensilestrengthandelongationoftheweldedjointsincreasedfirstandthendecreasedwiththedecreaseofdeepcryogenictreatmenttemperature.Theoptimaldeepcryogenictreatmenttemperaturewas-80℃,andthetensilestrengthandelongationoftheweldedjointswere222.5MPaand10.2%,respectively,whichweremuchhigherthanthoseoftheuntreatedweldedjoints.Conclusion:Inconclusion,deepcryogenictreatmentcansignificantlyimprovethemicrostructureandmechanicalpropertiesofAZ31magnesiumalloyTIGweldedjoints.Thebestdeepcryogenictreatmenttemperaturefortheweldedjointsis-80℃,whichcaneffectivelyreduceweldingdefectsandimprovethetens