TWI is working with industry to provide joining solutions for magnesium die castings in the automotive, electronics and aerospace sectors. Recent work has developed high productivity techniques for joining magnesium to aluminium and steel.
Magnesium alloy die-castings are increasingly being used in automotive structures, from seats and doorframes to I beams. They are also found more often now for electronic housings like notebook computer cases. These materials offer dramatic weight savings and allow production of single part complex structures with commensurate savings in fabrication costs.
However, magnesium alloy components present joining difficulties when integrating the die-castings into the rest of the structure, particularly where joints between magnesium and aluminium or steel are required.
While many magnesium alloys can be fusion welded, such techniques cannot produce sound welds when joining magnesium to other metals.
The only method currently available for completing such joints is bolting, but this adds weight and cost, requires accurate alignment and can create problems of fretting and wear between the bolt and the softer magnesium alloy. Alternative methods of joining magnesium to dissimilar metals are essential if the cost of using lightweight magnesium components is to be reduced and weight savings maximised.
Two technologies have recently been demonstrated at TWI that offer a potential answer. Seam welds are possible using friction stir welding. Although development of the process for magnesium to aluminium alloys is at a very early stage, initial trials show great promise.
For point joints, TWI has shown the feasibility of clinching and self-piercing riveting for joining magnesium alloy die-castings to steel and aluminium alloy sheet. Ordinarily, these processes cannot be used for joining magnesium die-castings due to their low ductility.
However, a Joint Industry Project led by TWI has overcome these problems and succeeded in achieving good mechanical and promising corrosion performance for a group of alloys, including AM60 and AZ91 magnesium alloys, 6111 and 5182 aluminium alloys and Zn-coated drawing steel.
The next stage of the work is to industrialise the process for high productivity application in a production environment. The new project is open to participants who will also receive all the data of the previous work. Participation will ensure that the technology is suitable for application for your own components and will ensure a technological lead in die-cast magnesium alloy assemblies.
Self-piercing riveting also offers the ability to set a threaded or shaped head into magnesium. So, attachments for fixing trim in place or for screw fittings can also be attached to magnesium die-castings using technology developed in TWI's Joint Industry Project.
Recent and ongoing projects on magnesium alloys at TWI include:
- Joining to steel and aluminium
- Laser welding
- Friction stir welding
In addition, TWI has performed confidential work for single clients and is a participant in the European MAGJOIN programme.
For further details contact Lee Smith or Philip Threadgill.