The Cu/Nb Ratio Influencing Microstructure, Mechanical and Electrical Properties in As-cast Al-3Cu-xNb Alloys

In this work, solidification experiments were performed with Al-3CuxNb alloys ( x = 0.5, 3 and 5wt.%). The role of the Cu/Nb ratio was investigated on thermal parameters such as growth and cooling rates ( V L and T R ), structure, microhardness (HV) and electrical properties such as electrical resistance, resistivity and conductivity ( R , ρ , and σ , respectively). A columnar to equiaxed grain transition (CET) was observed for lower Cu/Nb ratios. The typical solidification microstructure was quantified by means of secondary dendritic spacings ( λ 2 ). It was observed that the decrease of the Cu/Nb ratio with the increase of the Nb content increased the HV, R , and ρ values, but the σ values decreased. It was deduced that the harder particles of the Al 3 Nb and Al 2 Cu intermetallic phases contributed to the increase of HV, while the Al 3 Nb phase influenced the decrease of electrical conductivity with the increase of Nb content.