Fabrication Of Magnesium-Aluminum Composite Plates By Direct Hot Pressing And The Laminate-Interface Structures And Properties

Poor corrosion resistance of magnesium and magnesium alloys is one of the main reasons that prevents them from wider applications in many fields. In contrast, aluminum and aluminum alloys have excellent corrosion resistance and plastic formability. Their surface can be self-repaired and paintable, and Al element is beneficial for the corrosion resistance of Magnesium. Thus, coating Mg alloy with Al on its surface can fabricate a kind of laminated composite plate that can not only protect Magnesium alloys from corrosion but also maintain the magnesium alloys'high specific strength and specific stiffness, excellent damping performance as well as electromagnetic shielding characteristics.In this paper, a composite plate of magnesium alloy (AZ31B) and a pure aluminum metal with the size of 100mm×100mm×2.4mm was produced successfully by using two kinds of Mg-Al eutectic alloys (Mg-62at.%Al and Mg-31at.%Al) as the solder, respectively, and hot pressing with the indenter at different temperatures 460℃,480℃and 480℃,500℃, respectively, under 30 MPa for 60s in atmosphere.X-ray nondestructive test indicates that bonding interface is integrity. No pore and incomplete fusion were detected. The scanning electron microscope (SEM) equipped with X-ray energy dispersive spectrscope (EDS) was used for observing the cross-sectional micro structures and analysing the components of the bonding interface of the specimens fabricated under different process parameters. The results show that obvious diffusion occurs between the solders and the base plates, and a metallurgical bonding was achieved. When using Mg-Al eutectic alloy powder as solder, laminated interface of composite plate is composed of a-Mg+Mg17Al12 two-phase layer, Mg17Al12 single phase layer and Mg2Al3 single phase layer consecutively from AZ31B substrate to 1050 substrate, while when using Al-Mg eutectic alloy powder as solder, the laminated interface is composed of Mg17Al12 single phase layer and Mg2Al3 single phase layer consecutively from AZ31B substrate to 1050 substrate.The bonding strength was tested by tensile test, and the fracture surface was analyzed by SEM and X-Ray diffractomer (XRD). The interface strength as high as 24 MPa was obtained, and it was indicated that the fracture always occurs in a thicker intermetallics layer. The thick intermetallic compound layer in the laminated interface, especially, the Al3Mg2 layer is the weak link of the bonding where fracture is prone to occur. Mg2Al3 layer is thinner when using a-Mg+Mg17Al12 eutectic alloy as solder than that when using a-Al+Mg2Al3 eutectic alloy, and the interface bonding strength is relatively higher. Electrochemical tests show that corrosion resistance of Mg-Al composite plate is greatly improved compared to that of Mg alloys. The corrosion current of Mg-Al composite plate is same to that of the pure Al in 3.5wt.% NaCl solution.Besides, AZ31B-Zn-Al composite plate was fabricated using Zn plate as the interlayer (solder) with the hot indenter heated at 440℃holding for 30 s and under pressure of 15MPa lasted for 60 s. It was found that a violent reaction occurred between the interlayer and AZ31B substrate, but no reaction occurred on the side of the Al substrate. In this case, the plates was mechanically bonded and the bonding strength was much lower.