Influence of Heat Treatment on Gas Metal Arc Welded Aluminum 6063 Alloy for Automotive Aluminum Spaceframe Architectures

An aluminum structure has many advantages over steel for automotive application, but the combination of lower weight, with high torsional stiffness and good energy management performance in crash is perhaps the most beneficial. Hybrid architectures, consisting of a combination of aluminum products including stampings, extrusions (straight and hydroformed) and castings, are becoming more common. The Ford GT represents the first Ford Motor Company hybrid aluminum spaceframe. The frame is comprised of castings, extrusions and stamped, flat and roll-bonded, panels. All structural connections between the extrusions and the castings are fusion welded with the exception of the front and rear crush structures. Ford R&AE supported the Ford GT program in the joining and assembly of the hybrid aluminum body architecture, with responsibility for the development of the Gas Metal Arc Welding (GMAW) process. Recognizing that the heat input from the GMA welding process is significant, it is necessary to understand the aluminum material properties after temperature exposure during welding. The frame is subject to further temperature exposure during manufacture during the painting operations. Additionally, those areas of the frame around the engine will be exposed to high temperatures in service. The objective of this study, in support of the Ford GT, was to evaluate the mechanical properties of GMA welded 6063-T6 extruded coupons after different heat treatments simulating the paint ovens during vehicle build and extreme engine temperatures when in service. This information was critical for use in the program Finite Element Models (FEM) developed for Noise, Vibration, and Harshness (NVH), Crash and Durability. The study was successful in showing that the tensile strength of the welded aluminum was not affected by thermal exposure for the range of different temperatures and times, chosen to represent vehicle build and in service temperature conditions. The most consistent results were obtained for tests simulating the paint bake (180 °C for 30 minutes). The ‘as welded’ and engine bay temperature exposures (24 hour at 150 °C and 200 °C) showed higher variability. The failure mode for the 24 hour exposures was in the weld, as compared to the HAZ for the other samples.