Effect of the thickness of cold sprayed aluminium alloy coating on the adhesive bond strength with an aluminium alloy substrate

The variation of adhesive bond strength of cold sprayed 7075 and 7050 aluminium alloy coatings on 7050-T7351 Al alloy substrate with coating thickness was determined through shear and tensile tests. Generally, without heating the substrate, the shear bond strength decreases with the increase in cold sprayed coating thickness. The thickest 7075 cold sprayed coating produced on rectangular substrates, which were used to measure the shear bond strength, was 1.6 mm. Although thicker coating was produced on the end of the cylindrical substrates, which was used to measure the tensile bond strength in accordance with the ASTM C633 standard, increasing the coating thickness from 1.2 mm to 2.9 mm led to reduction in tensile bond strength from 10 MPa to 5.1 MPa. However, further increasing the coating thickness to 3.7 mm improved the bond strength due to the heating effect resulted from impact of the late stage spray on the pre-formed coating layers. When the rectangular substrates were heated at 175 °C during cold spray, not only much thicker coatings were produced, the shear bond strength was also significantly increased. Hence, heating cold sprayed substrate is considered as an effective approach to produce thick and highly bonded coatings.