Refining Effect of Trace Addition of B and the Impurity Elements in Al-Si-Cu-Mn-Ni Heat-Resistant Alloy on Primary Mn-rich Phase

Refining effect of trace B addition in Al-Si-Cu-Mn-Ni alloy on primary Mn-rich phase was studied by OM, SEM, TEM and HRTEM. Addition of trace B (0.02 wt%) remarkably alters the morphology of primary Mn-rich phase from coarse dendritic to fine short-rod-like or blocky, and significantly reduces its size. TEM/HRTEM characterizations clarify that the fine particles embedded in the short-rod-like or blocky Al3MnSi2 phase are (V,Ti,Mn) B2 phase. One good matching orientation relationship between Al3MnSi2 phase and (V,Ti,Mn)B2 phase is confirmed by E2EM model calculation, indicating that (V,Ti,Mn)B2 phase has a strong potential as the heterogeneous nucleation substrate for Al3MnSi2 phase during solidification. So, trace addition of B and the impurity elements in Al-Si-Cu-Mn-Ni alloy leads to the formation of fine (V,Ti,Mn)B2 particles that greatly enhances the nucleation of primary Al3MnSi2 phase and thus significantly reduces its size.