Effect Of Temperature Gradient Cyclic Pressing On Densification Of Spray Deposited SiC_p/7090 Aluminum Matrix Composite

As an advanced materials preparation technology, spray deposition has shown remarkable superiority in producing large-sized alloys and metal matrix composites. However, the spray deposited preforms usually contain a certain quantity of porosity. Besides, the oxide film on the surface of the particles leads to weak metallurgical bonding between the particles. In order to obtain an ideal structure and performance, densification and plastically deformation are needed further. Wedge pressing is a new technology of pressing, in which the large deformation can be obtained through the sum-up of local deformation and multi-step small deformation. In this thesis, temperature gradient is introduced to constant temperature wedge pressing, which solves the problem of abundant deforming in short transverse through constant temperature wedge pressing. The process is simplified through the technology of temperature gradient wedge pressing. Effect of gradient temperature wedge pressing and constant temperature wedge pressing on densification of Spray deposited SiCp/7090 composite is compared. The regularity of densifying for gradient temperat- ure wedge pressing is also studied. It is found that the problem that the degree of densifying is inadequate by once pressing in constant temperature wedge pressing is solved through gradient temperature wedge pressing. The research is vital not only to the further densification but also to the further research on plastically deforming. The conclusion of this thesis can be concluded as following:(1) By simulating the process of heating the billet, it shows that when the billet is heated for 90 minutes, the billet's temperature gradient is 136℃,which is perfect. It can be seen in the experiment that when the billet is heated for 90 minutes, the billet's temperature gradient is 180℃in the front face and is 250℃in the side face.(2) In the process of gradient temperature wedge pressing, the shape of the billet is"hyperbolic", and then the billet contacts the die wall absolutely. In the early stage of the process of gradient temperature wedge pressing, the flowing of the metal in the upper bed and the low bed of the billet is prior to the metal in the middle bed. In the intermediate stage and the anaphase the flowing of the metal balances, the whole of the billet is densified. In the process of constant temperature wedge pressing, the metal in the upper bed begins flowing firstly; the flow rate of the metal in the intermediate is greater than that in the anaphase. In the whole pressing process, the metal in the intermediate and the anaphase does not contact the die wall.(3) The maximum reduction in height is 25% in the two pressing process. The relative density of the sample plot in the process of gradient temperature wedge pressing is higher than that of the process of the constant temperature wedge pressing. It is found that the hardness is 117.3HB on the upper bed in the process of gradient temperature wedge pressing, while it is 118.3HB in the process of constant temperature wedge pressing. The hardness of the billet in the process of gradient temperature wedge pressing distributes uniformly, most of the hardness is more than 100HB. The hardness of the billet in the process of constant temperature wedge pressing distributes non-uniformly. The greatest hardness in the anaphase is 68.5HB.(4) In the process of gradient temperature wedge pressing, when the reduction of the billet in height is 5%, 15% and 25% respectively, the relative density becomes greater and greater along the pressure head moves in length. The relative density in the middle of the billet is minimum, the relative density in the edge is greater in width.(5) In the process of gradient temperature wedge pressing, when the reduction of the billet in height is 5%, the regularity of relative density distribution is found that the relative density in upper layer is the greatest, and the relative density is the least in the intermediate layer.(6) In the process of gradient temperature wedge pressing, when the reduction of the billet in height is 25%, the tensile strength is 304.52MPa and the elongation is 2.4%, the mechanical property is prior to that of constant gradient temperature wedge pressing. No evident pore can be seen in the fracture of the sample.