Research Of The Microstructure And Mechanical Properties Of The AM60/6061 And AM60/A390 Liquid-solid Bonding Interface

Aluminum alloys and magnesium alloys are important materials in the automotive industry. They have different advantages and disadvantages. Al alloys have great mechanical properties, while Mg alloys have smaller density. This paper systematically study on the Mg/Al (in detail AM60/A390 and AM60/6061) liquid-solid bonding samples to get a new material having the advantages both of Al alloys and Mg alloys.As is known to all, Al alloys and Mg alloys have the low melting points, and they easily react with oxygen on the surface and form oxide films. The oxide film on the Al surface is very dense, which prevents the metallurgical bonding of Mg and Al in the bonding process. This problem is solved by zincate immersion. Before the liquid-solid bonding experiments, we remove the oxide film and make the Al surface be covered with a layer of zinc film by zincate immersion. The result shows that the zincate immersion both can improve the wettability of 6061 and A390 by adjusting the zincate immersion process.We use a self-made device in the bonding process. We try and adjust pre-heat temperature and time to achieve the great effects of bonding. The result shows that the most appropriate pre-heat temperature and time are 650℃/95S and 700℃/140S for 6061 and A390, respectively.Through testing the microstructure of the AM60/6061 and AM60/A390, it is found that the AM60/6061 sample interface has five layers, in detail, α-Al、α-Al+β-Al3Mg2、 β-Al3Mg2+γ-Mg17Al12、γ-Mg17Al12+8-Mg and 8-Mg. While the AM60/A390 sample interface shows a network stucture and there is a Mg2Si layer close to Al. This Mg2Si layer prevents the diffusion of Al and Mg. This is the reason why the AM60/A390 interface has less intermetallic compound than the AM60/6061 interface. The shear strength test shows that the AM60/6061 samples just get about 10-20MPa, which is lower than the 30-40MPa of the AM60/A390 samples.In this paper, we try to improve the AM60/A390 interface microstucture and shear strength by adding 1.3 wt.% Ca element in the molten Mg alloy. The result shows that the 1.3 wt.% Ca addition in the molten Mg will effectively decrease the interface width and make the β-Mg17Al12 network structure undevelopment. There are two possible reasons.1.Al-Ca intermetallic compound (Al2Ca) can act as the heterogeneous nuclei of Mg, supplying more Mg nuclei amount.2.The enriched Ca on the P-Mg17Al12 grain boundary may prevent the β-Mg17Al12 grain growth. The shear strength test shows that the sample with 1.3 wt.% Ca addition in the molten Mg alloy has a 18.6% improvement, compared with the sample without Ca addition, and the shear strength reaches 45.2 MPa.Besides, heat treatment brings a further improvement for the microstructure and shear strength of the AM60/A390 samples. The result shows that the heat treatment makes the width of the AM60/A390 interface have a further reduction for the solid solution, and make the Mg2Si layer structure disperse into pellets for the different diffusion rate of Mg and Si in the different area. The shear strength is substantially improved after the heat treatment, about 21.9% more than that without heat treatment, reached 55.1 MPa.