Improvement of TiAl Alloy Sheath for Aluminum Alloy Castings and Its Application in Large Deformation Plate Rolling

[Technical field]

0001] The invention belongs to the field of TiAl alloy rolling processing, in particular to an improved rolling cladding and a rolling method of TiAl alloy using the improved cladding.

[0002] TiAl alloys have harsh hot working conditions because of their inherent brittleness. Once the mechanical state deteriorates during high temperature deformation, such as tensile stress, TiAl alloys are prone to crack and fracture. The temperature range of TiAl alloy which can be deformed smoothly at high temperature is very narrow. Hot working of TiAl alloy is carried out under isothermal conditions, and the cost of hot working under isothermal conditions is very high, so it is difficult to produce on a large scale. Therefore, the rolling of TiAl alloy generally adopts the quasi-isothermal rolling method of wrapping TiAl alloy slab with metal material under the constraints of ordinary rolling mill. The advantage of this method is to keep the processing temperature of slab by using wrapping. The wrapping material and TiAl alloy can obtain good mechanical state, such as compressive stress, when the strength compatibility of wrapping material and TiAl alloy is high in the hot working process. Because of the use of ordinary rolling mills instead of isothermal rolling mills, the cost has been greatly reduced and large-scale production can be formed. Based on the consideration of heat preservation, the existing envelope is designed with full thickness and large thickness, that is, the thickness of the envelope is the same in the three directions of length, width and height, and the thickness of the envelope is 3?4 times that of the plate. However, there are two shortcomings of the existing sheath. One is that the fully equal thickness design in three directions does not take into account the actual temperature distribution characteristics of the workpiece in the process of high temperature rolling and wastes the sheath material. The other is that the large thickness design makes the sheath material and slab material not match well in the process of high temperature rolling, thus the slab material is in a disadvantageous stress state and easy to crack.

[0003] Based on the brittle and difficult deformation characteristics of TiAl alloy, the existing TiAl alloy rolling process adopts the multi-pass rolling method with small deformation (between 5% and 10%). The disadvantage of this multi-pass rolling process with small deformation is that the deformation can not be easily carried out, and the temperature field of the slab changes alternately from high temperature to low temperature and then to high temperature due to multi-pass rolling. The stress state of slab tends to deteriorate due to repeated deformation of cladding and slab. For TiAl alloy which is difficult to deform, the probability of slab rupture is increased and the cost of rolling is increased.