This project, part of TWI’s Core Research Programme, aims to reduce the dependence on wet chemical processes as a pre-treatment to adhesive bonding of metals by replacing the etching chemicals with cold atmospheric plasma (Figure 1). This process successfully increased the lap shear strength of 316 stainless steel from 33 MPa (untreated) and 44 MPa (grit blasted) to 51 MPa (grit blasted and CAP treated), while a grit blasted and acid etched joint failed at 46 MPa (Figure 2). This was achieved while maintaining the joint’s mechanical properties and limiting the use of wet chemicals to solvent degreasing only
Overcoming inefficiencies
When metals are bonded using current methods, they are pre-treated using wet chemicals and energy-intensive processes. There are significant disadvantages to these processes, such as high energy demands, hazardous waste generation, and associated health and safety concerns.
A further issue is that each metal generally requires a different etch solution. This can limit design choices or increase the cost of manufacture considerably, requiring several chemical baths. CAP has the ability to treat different materials, with only a modest change in plasma chemistry required between each. The plasma has also the potential to be monitored to ensure that it meets specification during the treatment.