When selecting parting surface for aluminum alloy forgings, in addition to the same factors as those for steel forgings, uniform deformation shall also be specially considered. If the selection of parting surface is not reasonable, it is easy to make the streamline of forgings disordered. After the burrs are removed, the end of streamline is exposed, and aluminum alloy forgings are more likely to have defects such as through flow and through rib cracks on the parting surface, thus reducing their fatigue strength and stress corrosion resistance. Ideally, the parting surface is formed by backward extrusion, and the streamline is distributed along the shape of the forging. The parting surface is formed by forging, and the inner corner is easy to fold, flow through and the grain structure is uneven.
The surface oxidation, pollution and metallographic structure change of aluminum alloy forgings during forging are not obvious, so the machining allowance should be smaller than that of steel, titanium alloy and superalloy. Aluminum alloy has great adhesion. In actual production, a die forging slope of 7 ° is usually used to facilitate feeding. If there is a ejection device, 1 °~5 ° can also be used.
For aluminum alloy forgings, the design of fillet radius is particularly important. Small fillet radius not only makes metal flow difficult and fiber fracture, but also makes forgings fold and crack, reducing the service life of forgings. Therefore, the fillet radius should be increased as much as possible. The fillet radius of aluminum alloy forgings is generally larger than that of steel forgings. In order to prevent aluminum alloy forgings from cracking on the parting line after cutting, the height of rough edge groove bridge and fillet radius of forgings are 30% larger than those of steel forgings.
Aluminum alloy forgings are not suitable for rolling and drawing dies. Because in rolling and stretching blank, it is easy to produce cracks inside blank. Generally, single die forging is adopted. Especially for forgings with complex shapes, multiple sets of dies and multiple die forging shall be used. The blank with simple shape is gradually transferred to the forging with complex shape, so that the metal flow is uniform, the filling is convenient, and the fiber is continuous. Due to the large adhesion and poor fluidity of aluminum alloy, the working surface of the mold needs to be carefully polished. The wear direction is along the direction of metal flow, and the roughness of the working surface of the mold is above 1.6. In order to reduce the surface thermal stress on the working surface of the forging die, facilitate the flow of metal, fill the die, and ensure the final forging temperature, the die must be preheated before working at 250-400 ℃.