Effect of Additional Element on Weld Solidification Crack Susceptibility of Al-Zn-Mg Alloy (Report II) : Results of Weld Crater and Bead Cracking Tests(Materials, Metallurgy & Weldability)

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Crack susceptibility of weld crater and weld bead of synthesized-weld-metal Al-2%Zn-3%Mg-0.1 %Zr alloy with and without Zr, Ti and/or Ti+B (Ti with B) have been evaluated by means of GTA spot weld crater and Houldcroft-type weld bead cracking tests, respectively. Crack susceptibility of weld crater of synthesized-weld-metal alloy was reduced enough with more addition than 0.36%Zr, 0.14%Ti or 0.07%Ti+B in this experiment. Macrostructural investigation revealed that crack susceptibility of weld crater depended on grain refining effect of these additional elements and it was decreased as decrease in grain size almost independently of the kind of additional element. Among these additional elements, however, only Zr showed the marked beneficial effect to reduce the crack susceptibility of weld bead with more addition than 0.24%Zr. This beneficial effect of Zr was closely related with grain refinement of weld bead structure. There were no beneficial effect of Ti or Ti+B addition up to 0.83% or 0.49% respectively to reduce the crack susceptibility of weld bead in spite of fine equiaxed structure of weld bead in this experiment. Consequently, it was proved that Zr was the most beneficial additional element to reduce the crack susceptibility of both weld crater and weld bead, and Ti or Ti+B were almost no effect to reduce the weld bead cracking, though they showed remarkable effects to reduce the weld crater cracking.
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