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The proposed paper aims at the development of extruding seam square tube of AA7075 high strength aluminum alloy by simulation and experiment. There are several factors related to extrusion load such as billet temperature, billet dimension, flow stress, die cavity and product geometry. The extrusion loads and die stresses for hot extruding square tube with respect to different product have been investigated. Since AA7075 behaves high forming resistance comparing to AA6063 and AA6061, the product design and die design should be modified in order to meet with the limitation of extrusion machinery. Moreover, AA7075 has high thermal welding crack behavior by comparing to AA7003. Therefore, In order to provide high contact pressure enough to conduct solid welding for the split AA7075 materials in welding chamber, the specific die cavity design has been finished. Then, the solid welding pressure can be increased. The research results show that under the same forming conditions such as fixed ram speed and billet temperature, the extrusion force for the product with thick thickness is small than the one with thin thickness. The same result was obtained for die stress. A square tube extrusion experiment has been conducted by installing die set into forward extrusion machinery. The experiment and simulation results have been compared and discussed.

Direct extrusion by porthole – bridge die configuration has been successfully used to fabricate products with hollow cross sections for 6000 series aluminum alloys. However, if for 7000 series aluminum alloys, this situation alerts since different alloy composition such as Cu causing hollow extrusion failed due to not enough welding strength in seam. In order to determine the solid welding conditions during hollow extrusion with porthole die structure for high strength aluminum alloy, an easy tooling configuration has been designed. The proposed method is easy and cheap because there is no necessary to conduct experiment in controlled environment such as in vacuum chamber of Gleeble test or in a protective atmosphere. A seam and hollow extrusion for square tube has been conducted to obtain the welding strength comparison to the proposed solid welding method which shows good agreement.

AA7075 has many good mechanical properties; however, its bonding strength is poor and is difficult to produce extruded hollow products. Although some researchers proposed different method to study welding strength of Aluminum alloy, related study for high strength Aluminum alloy in hollow extrusion process is not enough. This study use DEFORM 3D finite element analysis software to simulate two different types of hollow extruding die configurations for square tube extrusion process, namely: type I welding position at the corners of the square tube and type II on the side faces. The welding strengths of these two kinds of extruded tube are studied by expanding test and tensile test. The service lives of these two extrusion die components are studied based on the die stress and die wear information. Some information about the study are as follows: ingot material is AA7075, ingot diameter is 127mm, the extruded tube outside dimension is 54mm × 54mm, thickness is 5mm, extrusion temperature is 480°C, and ramp speed is 0.5mm/s, die material is SKD61 with HRC48. Research results show that the maximum extrusion force for type II is greater than type I. The maximum equivalent die stress occurs in upper die rather than in lower die both for type I and II. However, the predicted die life for type II is greater than type I due to extrusion die design. The welding strength for type II square tube is about 300 MPa on each welding seam.Copyright © 2012 by ASME