Interfacial Microstructure Evolution Of Al/Mg/Al Laminates Fabricated By Two-pass Hot Rolling And Influences Of That On Mechanical Properties

In recent years, magnesium alloy compared with other light alloy materials is favored by transportation, communication and aerospace industry because of its benefits of low density, high specific strength, vibration reducing performance, high-thermal conductivity, electro-magnetic shielding and ease of recycling. However, magnesium alloys have poor corrosion resistance, which have limited their widespread applications. Aluminum and aluminum alloy, by contrast, have good corrosion resistance, plastic forming properties, excellent surface paintability, meanwhile aluminum element additive improves the corrosion resistance and mechanical properties of magnesium. Thus, the poor corrosion resistance, can be overcome by coating aluminum on the surface. By this way, the performance advantages of both aluminum alloy and magnesium alloy can be utilized simultaneously. Usually, a large reduction in thickness, resulting from a large plastic deformation, is needed to bond a magnesium alloy plate and an aluminum alloy plate by rolling. An enhanced bond requires a greater reduction in thickness. However, the ductility of most magnesium alloys is not enough to permit such a large strain deformation at room temperature. Magnesium alloys are very prone to oxidation, especially at high temperatures. Thus, it is inevitable that the surface of a magnesium plate will oxidize during the preheating prior to rolling. Heating at a lower temperature is beneficial for a magnesium plate to ensure a clean surface and to achieve a strong bond with the aluminum plate.In this paper, a two-pass hot rolling method was developed, which can be expected to be more practical for producing Al(5052)/Mg(AZ31)/Al(5052) laminated composite plates by controlling the different hot rolling temperature and reduction ratio. In the first pass, the Mg alloy plate and Al alloy plate were preheated for15minutes at the temperature of350℃in the heating device, then the rolling was carried out with the reduction ratio40%, after that the clad plate obtained by one pass rolling was heated again for10minutes at the temperature of400℃in the heating device, finally the second pass rolling was performed with the reduction ratio35%.Microstructural examinations show that no new phases formed at the bond interface after the first hot rolling pass. However, at the direction perpendicular to hot rolling direction, a continuous distribution Mg17Al12and Al3Mg2intermetallic compounds layer was formed at the joint interface. While in the hot rolling direction, the continuous intermetallic was broken into fragments that are intermittently dispersed at the bond interface after the second hot rolling pass. Although cracks originate from the metallic compound zone, the broken metallic compound layer limited fracture propagation, so the interface bonding performance was enhanced.The growth of the intermetallics layer follows the parabolic low, and from this, the kinetic equation for the growth of the intermetallic compound layers is established. The diffusion coefficient and the growth rate increase with rising annealing temperature, whereas the incubation time decreases with rising temperature. No obvious intermetallic compound layers are observed when the annealing temperature was200℃or below, even after holding time of24hours.Fabricating of Al/Mg/Al laminates undergone the process of preheating before rolling, the first pass rolling, the second time preheating, the second pass rolling and annealing at low temperature, at the same time, interfacial microstructure undergone a series of evolution process.