مقاله جوشکاری با عنوان :Resistance Spot Welded AZ31 Magnesium Alloys, Part II:Effects of Welding Current on Microstructure and MechanicalPropertiesL. LIU, L. XIAO, J.C. FENG, Y.H. TIAN, S.Q. ZHOU, and Y. ZHOUچکیده:Resistance spot welding of AZ31 magnesium alloys from different suppliers, AZ31-SA (fromsupplier A) and AZ31-SB (from supplier B), was studied and compared in this article. Themechanical properties and microstructures have been studied of welds made with a range ofwelding currents. For both groups of welds, the tension-shear fracture load (FC) and fracturetoughness (KC) increased with the increase in welding current. The FC and KC of AZ31-SA weldswere larger than those of AZ31-SB welds. The fracture surfaces of AZ31-SB welds were relativelyflatter than those of AZ31-SA. Microstructural examination via optical microscopedemonstrated that almost all weld nuggets comprised two different zones, the columnar dendriticzone (CDZ), which grew epitaxially from the fusion boundary, and the equiaxed dendriticzone (EDZ), which formed in the center of the nugget. The nature and extent of the CDZseemed to be critical to the strength and toughness of spot welds because of its position adjacentto the inherent external circular crack-like notch of spot welds and the stress concentration inthis region. The width and microstructure of the CDZ were different between AZ31-SA andAZ31-SB. The AZ31-SA alloy produced finer and shorter columnar dendrites, whereas theAZ31-SB alloy produced coarser and wider columnar dendrites. The width of the CDZ close tothe notch decreased with the increase of current. The CDZ disappeared when the current washigher than a critical value, which was about 24 kA for AZ31-SA and 28 kA for AZ31-SB. Themicrohardness of the two base materials was the same, but within the CDZ and EDZ, thehardness was greater in AZ31-SA than AZ31-SB welds. It is believed that the different microstructuresof spot welds between AZ31-SA and AZ31-SB resulted in different mechanicalproperties; in particular, KC increased with the welding current because of the improvedcolumnar-to-equiaxed transition.
مقاله جوشکاری با عنوان :Resistance Spot Welded AZ31 Magnesium Alloys, Part II:Effects of Welding Current on Microstructure and MechanicalPropertiesL. LIU, L. XIAO, J.C. FENG, Y.H. TIAN, S.Q. ZHOU, and Y. ZHOUچکیده:Resistance spot welding of AZ31 magnesium alloys from different suppliers, AZ31-SA (fromsupplier A) and AZ31-SB (from supplier B), was studied and compared in this article. Themechanical properties and microstructures have been studied of welds made with a range ofwelding currents. For both groups of welds, the tension-shear fracture load (FC) and fracturetoughness (KC) increased with the increase in welding current. The FC and KC of AZ31-SA weldswere larger than those of AZ31-SB welds. The fracture surfaces of AZ31-SB welds were relativelyflatter than those of AZ31-SA. Microstructural examination via optical microscopedemonstrated that almost all weld nuggets comprised two different zones, the columnar dendriticzone (CDZ), which grew epitaxially from the fusion boundary, and the equiaxed dendriticzone (EDZ), which formed in the center of the nugget. The nature and extent of the CDZseemed to be critical to the strength and toughness of spot welds because of its position adjacentto the inherent external circular crack-like notch of spot welds and the stress concentration inthis region. The width and microstructure of the CDZ were different between AZ31-SA andAZ31-SB. The AZ31-SA alloy produced finer and shorter columnar dendrites, whereas theAZ31-SB alloy produced coarser and wider columnar dendrites. The width of the CDZ close tothe notch decreased with the increase of current. The CDZ disappeared when the current washigher than a critical value, which was about 24 kA for AZ31-SA and 28 kA for AZ31-SB. Themicrohardness of the two base materials was the same, but within the CDZ and EDZ, thehardness was greater in AZ31-SA than AZ31-SB welds. It is believed that the different microstructuresof spot welds between AZ31-SA and AZ31-SB resulted in different mechanicalproperties; in particular, KC increased with the welding current because of the improvedcolumnar-to-equiaxed transition.