Microstructure, mechanical properties and corrosion resistance of A356 aluminum/AZ91D magnesium bimetal prepared by a compound casting combined with a novel Ni-Cu composite interlayer.

In the present work, a novel Ni-Cu composite interlayer was prepared on the surface of A356 aluminum alloy solid insert using the chemical nickel-plating and electro-coppering technology, in order to restrain the generation of brittle phases and enhance the shear strength of A356 aluminum/AZ91D magnesium bimetal manufactured using a compound casting. The effect of the Ni-Cu composite interlayer on the microstructure, mechanical properties and corrosion resistance of the bimetal was studied. The results show that the Ni-Cu composite interlayer effectively restrained the generation of the brittle and hard Al-Mg intermetallic compounds (IMCs). The interface layer of the A356/AZ91D bimetal without Ni-Cu composite interlayer was composed of Al 3 Mg 2 , Al 12 Mg 17 , δ-Mg and Mg 2 Si phases, while the interfacial reactants of the A356/AZ91D bimetal with Ni-Cu composite interlayer were mainly Al 3 Ni, Ni (Cu), Cu (Ni), Mg 2 Cu and Al 7 Cu 3 Mg 6 phases. With the application of the Ni-Cu composite interlayer, the thickness of the interface of the A356/AZ91D bimetal remarkably decreased from 1400 μm of the sample without Ni-Cu composite interlayer to 40 μm. The shear strength of the A356/AZ91D bimetal using Ni-Cu composite interlayer increased by 20.3 % compared with that of the bimetal without Ni-Cu composite interlayer. The fractures of the A356/AZ91D bimetals with and without Ni-Cu composite interlayers belonged to a brittle rupture mode. The breakage of the bimetal with Ni-Cu composite interlayer mainly took place between the Ni-Cu layer and AZ91D matrix, while the rupture of the A356/AZ91D bimetal without Ni-Cu composite interlayer was located in the interface layer. The Cu(Ni) and Ni(Cu) layers had a lower nano-hardness than the Al-Mg IMCs, and the elasticity modulus for the Cu(Ni), Ni(Cu) and Al 3 Ni phases were higher compared to those of the Al-Mg IMCs. The results of corrosion test exhibited that the Ni-Cu composite interlayer had little influence on the corrosion resistance of the A356/AZ91D bimetal. [ABSTRACT FROM AUTHOR]