Connect, no. 150, September/October 2007, p.1
Joining dissimilar materials is a topic of extensive interest in manufacturing particularly in the automotive sector where the benefits of using lightweight materials such as magnesium and aluminium alloys can help to reduce vehicle body weight for improved fuel efficiency and lower greenhouse gas emissions.
Fusion welding between magnesium and aluminium alloys results in undesirable brittle intermetallics which limit the resulting weld quality. Consequently, there is a drive to improve existing techniques and develop new methods for joining such dissimilar lightweight materials. The first stage of the development of a new method to join these materials has been successfully completed by TWI's Laser and Sheet Processes Group.
This work was achieved by welding two sheets of the same material and interlocking the second material between these sheets.
In the trials at TWI, holes were machined in a magnesium sheet which was then sandwiched between two aluminium sheets.
Using a 3 kW Nd:YAG laser, a spot weld was produced by focusing a 1mm diameter laser spot on the surface of the top aluminium sheet, directly above the position of the hole in the magnesium sheet ( Fig.1). The laser beam fused together the two aluminium sheets and the central magnesium sheet became interlocked between the top and bottom sheets.
The resulting joints were tensile tested; the best of these achieved a shear stress of 70% of the shear stress of Al/Al welds. Further work in this area would aim to increase the strength of the joint by the use of a filler material to avoid the typical sunken top bead as seen in Fig.2.
The use of laser processing to form a mechanical joint shows promise and could be a valuable weapon in the fight for low-cost joining methods to lightweight components and vehicles. The method is not restricted to aluminium/magnesium but can be applied for any pair of dissimilar materials.
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