Effect of Pre-treatment of the Surface of Aluminum Alloy on the Properties of Adhesive Joints

Field: Engineering (Physical Sciences)

Abstract

Pre-treatment of surfaces before adhesive bonding of aluminum alloy materials is used in many industrial applications, most often in the automotive industry, railway industry, aviation industry, food industry, chemical industry, construction industry and others. The strength of adhesive bonded joints and their properties can be affected by various factors such as surface cleanliness, degree of greasing, corrosion attack, surface roughness, surface wettability or various surface pretreatment technologies. Appropriate surface pretreatment technologies were chosen for the research, which provide us with the best possible conditions for adhesive bonding. Technology of mechanical pretreatment of surfaces by grinding, blasting with abrasive brown corundum and dry ice. Technology of chemical pretreatment of surfaces by degreasing with isopropyl alcohol and pickling. Physical technology of surface pretreatment by laser and plasma cleaning. Pretreatment of the surface using pyrolytic application of amorphous silicon dioxide - Pyrosil and the technology of anodic oxidation ELOX of aluminum alloys. Bonded joints were created from aluminum alloy EN AW-5754 with a hardness of H22, on which evaluation of the strength properties of adhesive bonded and hybrid joints were performed. The research consisted in the fact that when using the same sample materials and the same appropriately selected type of adhesive 3M™ Scotch-Weld™ Flexible Acrylic Adhesive DP8625NS, different pretreatments of the surfaces affect the strength of the bonded joints. The joints were tested with a shear test and the types of failure of bonded and hybrid joints were evaluated. The result was an evaluation of the strength of adhesive bonded and hybrid joints with various surface pretreatments. Surface pre-treatments for hybrid joints were chosen to be the same as for adhesive bonded joints. Some samples were cleaned and a fingerprint was added to the sample to simulate a possible failure due to mishandling of the products. It was found that the highest pull-out strength was achieved for the hybrid-bonded specimens that were pre-treated using isopropyl alcohol degreasing, pneumatic blasting with brown corundum abrasive, and ELOX anodic oxidation of aluminum alloys. The addition of a rivet to the joint improved the strength properties in all hybrid joint cases. In the hybrid joint, it is possible to combine the excellent strength properties of the adhesive and quick fixation with a rivet. The highest strength of the hybrid joint was achieved by pre-treating the surface by pneumatic blasting with abrasive brown corundum. The highest pull-off forces for adhesive bonded samples were achieved by pre-treatment of the surface by means of grinding followed by degreasing with isopropyl alcohol, pneumatic blasting with abrasive dry ice and by cleaning with a laser beam. Although the samples cleaned with laser beam achieved a slightly lower strength than with grinding, these are the best cleaned samples. The Pyrosil technology fared the worst, achieving the lowest strengths. Samples contaminated with fingerprints after pretreatment of the surfaces, a lower bond strength in some cases by up to 20% was found. This determined to what extent contamination would affect bond strength and whether any of the methods were more sensitive to contamination than others.