Effect of Cu Addition on Properties of an Al-La Alloy

Abstract

The effect of copper content on the microstructure and properties of an aluminum copper alloy containing lanthanum was studied by adding 0.5 wt% lanthanum and different contents of copper to the 2A12 alloy. We used a universal testing machine, Brinell hardness tester, and friction and wear testing machine to test the mechanical properties of the alloy. The microstructure and phase composition of the alloy were analyzed using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The results show that, after adding La and Cu, the alloy grain is refined, and the fracture mode changes from dissociation fracture to quasi dissociation fracture. A new phase containing La accumulates at the grain boundary. If the amount of Cu added is too large, the tendency for hot cracking increases, which can easily lead to the formation of voids or even cracks. The tensile strength and hardness of the cast alloy significantly increase with the increase in Cu addition. In the range of adding 2 wt% to 5 wt% Cu, the tensile strength and hardness of the cast alloy increases by approximately 12% and 17.84%, respectively, compared with the original alloy. With the increase in Cu addition, the elongation of the alloy first increases and then decreases, reaching its maximum value when Cu addition is 3 wt%. Adding Cu is beneficial for improving the wear resistance of the alloy. When the addition of Cu is 3 wt%, the alloy has the best wear resistance and minimum wear amount. This is due to the enrichment of La and Cu at the grain boundaries, forming new La phases or other phases with higher hardness, which changes the properties of the alloy. It shows that the content of Cu in the 2A12 alloy can be increased to 7-8% with the increasing of additional rare-earth elements, and a new Al-Cu (7 wt% to 8 wt%)-Mg (1.2 wt% to 1.8 wt%)-Mn (0.3 wt% to 0.9 wt%)-La (0.5 wt%) alloy, in which tensile strength, hardness, and elongation of the alloy are increased by 8.1%, 16%, and 79.1%, respectively, can be formed. In addition, the wear resistance of Al-La alloys also improves significantly with the addition of copper content. The coefficient of friction is reduced by 68% compared with no copper addition.