深冷處理對AZ31鎂合金TIG焊接接頭組織和性能的影響中期報告摘要：本文研究了不同深冷處理（-60℃、-80℃、-100℃）對AZ31鎂合金TIG焊接接頭組織和性能的影響。研究結果表明，隨著深冷處理溫度的降低，接頭強度和延展率先升高后降低。最佳深冷處理溫度為-80℃時，接頭拉伸強度和延展率分別為222.5MPa和10.2%，遠高于未經深冷處理的接頭。同時，深冷處理可以有效減少接頭的氣孔和裂紋，提高接頭的成形性和可焊性。關鍵詞：AZ31鎂合金；TIG焊接；深冷處理；組織和性能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