The filler metal in arc welding is often different (dissimilar) from the base metal in composition. It can cause macrosegregation along the fusion boundary and/or at the weld bottom. Macrosegregation features include filler-deficient "beaches," "peninsulas," "islands," and filler-rich zones. Although such macrosegregation can degrade the weld quality, its formation is still not well understood.;In the present study, the liquidus temperatures of the weld metal (T LW), the base metal (TLB), the filler metal (TLF ) and the partially mixed filler metal near the pool bottom (T LF') were considered to explain how these features form. Based on the difference between TLW and TLB, four macrosegregation formation mechanisms have been proposed. Mechanisms I and II describe macrosegregation features when the filler metal is mixed well with the bulk weld pool, while Mechanisms III and IV describe those when the filler metal is partially mixed with the bulk weld pool.;To verify these four mechanisms, the binary Al-Cu, Al-Si, Ni-Cu and ternary Al-Cu-Si systems were selected, and welds were made by gas-metal arc welding. The experimental results verified the four mechanisms.
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