Abstract Scope |
Welding of battery trays for electric vehicles has been an ongoing challenge for the past years in the automotive industry worldwide, especially as far as the need for reproducible quality welding of long seams, low distortions and productivity were concerned. Our experimental research work focused on finding optimum friction stir welding tools and parameters to accomplish the highest welding speeds in joining Al extrusions to castings.
Welds made using traditional FSW tools were compared with different designs for probes made for traditional- and Stationary Shoulder SS-FSW in this experimental research. For the same weld quality, stir zone geometry and heat affected zone morphology and hardness were compared and mechanical testing of weld coupons were completed.
It was found that welding speeds of up to 6 m/minute were reproducibly reached in laboratory conditions, almost one order of magnitude greater than during welding with other FSW tool designs for the same sheet thicknesses. However, a very exact probe penetration control was required at higher downforces to achieve these results, something which might be difficult to implement in everyday industrial practices.
Due to the high rotational speeds of the probe used, higher local temperatures and a more pronounced softening in the stir zone were observed, when compared with traditional FSW. Additionally, some lack of bonding due to entrapment of surface oxide layers from the original extrusion surfaces were also found in SS-FSW welds. Several post-weld heat treatments were performed, followed by mechanical and corrosion testing.
It was found that improved tool design and parameter optimizations eliminated most eld quality problems. After overcoming additional part setup inaccuracies and downward force variations, it was concluded that high speed FSW welding can be readily used for high-productivity industrial welding of electric vehicle battery trays. Specific post-weld heat treatments were also recommended for increased mechanical strength and improved corrosion properties. |