Simulation And Experimental Study Of The Spray-formed Ultra-high Strength Aluminum Alloy Cylinder’s Anti-extrusion Process

The hot working of spray-formed ultra-high strength aluminum alloy is more difficult than traditional7000series aluminum alloy because of more alloying components. It is known that the deformation of cylinder is not well-distributed in extrusion process. So the reasonable mold structure and appropriate thermal processing is particularly important before the extrusion process. In this paper, the numerical simulation and experiment were combined to research the deformation behavior of spray-formed ultra-high strength aluminum alloy cylindrical workpieces in the anti-extrusion process. The appropriate process parameters of the cylinder were obtained and anti-extrusion process was proposed.The spray-formed alloy, the as-HIP (Hot isostatic pressing) treated and as-homogenized microstructure of spray-formed alloy were investigated by using metalloscope (OM) and scanning electron microscopy (SEM) technology. In the spray-formed alloy, the grain were equiaxed and approximately20-30μm and a lot of first precipitated phase existed in both the intragranular and grain boundary which are rich in Al, Zn, Mg and Cu. After HIP, it was densified and the density measured by drainage method was2.89g/cm3, which exceeded the as-cast aluminum of the same composition. The grains did not grow obviously and the second phase dissolved partly leaving a little in the grain boundary. After studies of homogenizing heat treatment was obtained to440℃/12h+472℃/24h.By the thermal compression tests, the constitutive equation of the experimental alloys after homogenizing heat treatment was:By plotting and analyzing the thermal processing diagram, this alloy has a relatively narrow hot working scope. The suitable processing temperature range was380℃-405℃, and the strain rate is not more than0.5s-1.The load velocity field, stress concentration and FLOWNET (flow lines) in the extrusion process were analyzed by the finite element simulation Deform-3D software. It was found that the deformation of the cylinder is not well-distributed in extrusion process, and the deformation at cylinder wall is much bigger than bottom. The extrusion load peaks stabled at around4500kN, and the highest peak load reached5500KN. Therefore, the extruder tonnage of550tons or more should be ensured. According to the flow characteristics during anti-extrusion process, the numerical simulation and experiment were adopted to optimize the shape of the billet and die. The result is shown that the average values of equivalent strain in the bottom increases after optimizing the shape of the billet and die. Comparing with the flat bottom billet and flat die, the average strain of the flat bottom billet and concave die, concave bottom billet and flat die, and concave bottom billet and die increase by26.6%,75.9%,89%, respectively. And the biggest deformation at cylinder bottom was gotten in concave bottom billet and die.The peak load of anti-extrusion process experiment approaches the simulation predicted values, and the maximum difference between them was about5%. The result of microstructure analysis of different position in the cylinder is shown that the cylinder bottom can be improved effectively by using the concave bottom billet and die.