Research On The Causes Of 7050 Aluminum Alloy Casting Rolling Plate Crack

7050 aluminum alloy with a high strength and high hardness, well weldability, hot workability, toughness and corrosion resistance have been widely applied to the aircraft, aerospace and military aspects. With the continuous development and progress of society, the amount of ultra-high-strength aluminum alloy applications in the aerospace industry and the military aspects of getting to the big, its performance materials(specific strength, specific stiffness, toughness, resistance to fatigue and corrosion resistance) also have higher requirements.Twin roll casting technology achieve the casting and rolling into one, shorten the process, reduce production costs and also achieve a continuous efficient and stable production. However, for the production of high alloy components thin slab such as 7050 aluminum, it is difficult to control the microstructure, segregation and the plate type accurately, surface prone to crack, tropical and uneven plate during the preparation, there will be serious when broken belt, leads to low timber, this is a certain lack of practicality.Object of this study is to 7050 aluminum alloy casting plate, using optical, SEM, EDS and other experimental methods for 7050 aluminum alloy casting slab crack at the macro and micro morphology. Then the causes of cracks is found by the theoretical calculations and using the casting and high temperature tensile test to explain the crack reason combined with theoretical calculation. The casting experiments is conducted by changing casting speed and the width of the roll gap, Identify the changes in both the process parameters on crack formation and organizational change. Experimental results show that:The crack of cast rolling produced at the surface is extended along the direction of equiaxed grain boundary, not transgranular. The energy spectrum shows there are elements of Fe exists in the cross section, The surface scanning at the surface crack displayed that the Zn elements in the crack is the enrichment phenomenon. Combining theoretical calculation with experiment that there is a temperature difference of center and surface thermal stress generated will reach the tensile strength has a tendency to crack.Casting speed is smaller and the roll gap width becomes larger reduce probability of crack,When the casting speed is slow and the roll gap width is small, a dendrite exist near the surface. When the casting speed is increased and the increase of the roll gap width, the organization are mostly the equiaxed grains. The second phase particles appeared at the grain boundary, In the rolling deformation, As the secondphase particles with a hard, brittle and non deformability,are generated at the grain boundaries, and they reduce the binding force between the grain boundary. With intergranular fracture, there will be cracks in the macro.