Al - Cu - Mg - Ag/ti Rolling Composite Interface And Al - Cu - Mg - Ag Alloy Friction Stir Welding Process

Al-Cu-Mg-Ag alloys and Pure Ti possesses high strength to weight ratio, superior high temperature properties and good wear-resisting property. The long-period serving temperature is up to250℃and300℃, respectively.The paper mainly investigates Al-Cu-Mg-Ag/Ti bimetallic composite produced by cold-roll bonding and the friction stir welding of Al-Cu-Mg-Ag alloy. The main conclusions can be summarized as follows:(1)Al-6%Cu-0.5%Mg-0.4%Ag/Ti bimetallic composite can be obtained by cold-roll bonding with44%rolling reduction in a single rolling pass.(2) Ti and Al elements occurs noticeable diffusion during the annealing treatment. And TiAl3is the first phase formed during the annealing process, because TiAl3has a formation Gibbs energy more negative at515℃than other intermetallics belonging to Ti-Al binary system. In addition, the increase of TiAl3layer is mainly toward the Al-Cu-Mg-Ag alloy side.(3) The whole annealing process can be divided into two stages. The first stage can be interpreted as TiAl3lateral growth parallel to the interface due to heterogeneous nucleation, followed by TiAl3coalescence to form a continuous layer on the interface. The second stage is a thickening of the continuous layer in the direction perpendicular to the interface. The formation of continuous TiAl3layer led by lateral growth is responsible for enhancement of the interlaminar shear strength at the first stage. The maximum interlaminar shear strength reaches about40MPa after annealing for12h. The thickening of TiAl3layer at the second stage leads to embrittlement of TiAl3layer, and resultant degradation of the interlaminar shear strength.(4) The tensile strength of bimetal composite are always between the values of the pure Ti and Al-6%Cu-0.5%Mg-0.4%Ag alloy during the test temperatures, and the tensile strength of the bimetal composite is consistent with the mixture rule. (5) Al-6%Cu-0.5%Mg-0.4%Ag alloy obtain good friction stir weld joint when rotational speed and welding speed are1200r/min and60mm/min, respectively. The tensile strength of FSW joint is409.5MPa, up to82.3%of the base metal value.(6) The structure of the friction stir weld joint is investigated. The dynamic crystallization produces fine and equiaxed grain in weld nugget zone. A distinct boundary emerges on the place which is between weld nugget zone and thermo-mechanically affected zone of the advancing side, and it exist lots of dislocations and subgrains in the thermo-mechanically affected zone. The grain and precipitate in the heat-affected zone occurs obvious coalescence. In addition, it occur the phenomenon that the Ω and θ’phases transform to θ phases, and the degree gradually increase with the distance shortening from the center of weld joint.