Investigation Of Preparation And Properties Of The 7075/6061 Bimetal Composite Materials

Bimetal composite has been widely used because of excellent comprehensive performance, but the microstructures with distribution characteristics “dendritic/dendritic”will be hard to deform, so its development is limited. The shortcoming can be overcome by the microstructure with “semi-solid microstructure/dendritic microstructure” distribution characteristics. The 7075/6061 bimetal composite ingots of lightweight, high strength,corrosion resistant have been prepared by the solid/liquid metal compound casting and7075 alloys are the semi-solid billets prepared by the strain-induced melt activation technology(SIMA). The microstructures and properties of semi-solid billets and bimetal composite ingots were analyzed and tested. The main conclusions were obtained as follows:During the properties of the semi-solid 7075 alloy by SIMA method, the effects of pre-deformation, isothermal temperature and holding time on the microstructures and compression properties have been investigated. The processing parameters are optimized:pre-deformation degree 10 %, isothermal temperature 610 ℃ and holding time 30 min.The 7075/6061 bimetal composite ingots of “semi-solid microstructure/dendritic microstructure” distribution characteristics were prepared by solid/liquid metal compound casting with semi-solid billet of 7075 alloy and melt of 6061 alloy. Cooling method has a great effect on compound ability of the ingots. The interface defects of microstructure and compound ability of the ingots through air-cooling were better than the ingots through water-cooling, and while the parameters are the outside melt temperature 760 ℃, the billet pre-temperature 200 ℃ or 300 ℃ and air-cooling the residual oxides and pore are reduced significantly. The ingots have the gradient distribution of alloy elements and rockwell hardness in cross section, the interfaces are semi-solid microstructure and dendritic microstructure, and the solid particles of the inside layer are more finer and rounder by metallurgical compounded. As the same conditions, the evolution rule of the semi-solid microstructures closed to the interface are spherical solid particles incorporating and growing, glomeration, non-glomeration and dendrite while the pre-heating temperature of the semi-solid billets and the outside melt temperature increase; The optimized casting parameters of the 7075/6061 bimetal composite ingot are air cooling, outside melt temperature 760 ℃, semi-solid billet preheating temperature 200~300 ℃.