Research On Semi-Solid Billet Of 6061 Aluminium Alloy By Sima And Its Thixo-Forming

Aluminium alloy is a kind of light colored metal which is widely used, it has high specific strength and high specific rigidity; it also has good electric conductivity and good conductivity for heat and its strain resistance is good too, so it is a ideal material for aviation equipment. In general, machining is used to fabricate complicated parts that can not be made by forging process. A quantity of raw material is thus wasted in a very long process cycle, resulting in high manufacturing cost. Semi-solid metal working, a newly developed process for near-net shaping complicated parts, with mechanical properties approach to those of forging parts, will establish a new method for making such complicated parts. Taking 6061 aluminium alloy as object, made it's billet by SIMA ( Strain Induced-Melt Activation ) method. The mechanical character and the simulation of it's shapping process are then studied which could be a reference of the thixo-mold experiment.In the first period, the semi-solid billet was preparated by SIMA method, and then it's equivalent stress and equivalent strain model was set up by compression tests. During the second period, mould of the shell shapped part in three dimension was set up using Pro-Engineer(Proe)software, and then the shapping process of the part was simulated by using the Deform3D software, so the effect of the mould fabric and the forging method to shapping the part was then gained. During the last period, the forging experiments were done which proved the results of the simulation, and the primary research on the forging process of the valve was finished.By observing the microstructure of the billet which was cold upsetted we found that cold upsetting method could fine the grain size on some degree. Through a large number of compression tests in 6061 aluminium's semi-solid state, mechanical behaviors during semi-solid deformation process for the 6061 aluminium alloy were investigated, and found that a larger deformation was realized under less force for cold upsetting state billet and this kind of billet is sensitive to temperature and strain rate. Through a lot of simulation tests, the extruding from the two side method can't forming the valve for the material extruded from the top method, the valve can be formed in liquid state but can't be formed in semi-solid state. If change the parting plan, then the valve without side hollows can be formed by direct extrusion method, if get rid of the cervix, then it can be formed by direct extrusion method with the parting plane in the biggest diameter position.The last solution is: form the valve without cervix by direct extrusion method and then machine the unwanted material.