Adhesion of epoxy compaund to aluminum bronze

The possibility to heighten the adhesion of the epoxy coating to metal surface by varying the hardener content was investigated. The experiments were conducted on the epoxy composition made up of modified epoxy resin K-153 and hardener (polyethylene polyamine). The prepared compositions contained the following percentage of the hardener: 6.1, 7.0, 7.7, 8.3, 9.5, 10.7, 11.9 and 13.0% by volume. Two series of the experiments were carried out. The goal of the first one was to evaluate the degree of the completeness of epoxy oligomers spatial stitching in hardening. The evaluation was indirect and consisted in measuring the acoustic impedance of the compositions. The second series was carried out to determine the adhesion of the epoxy compositions to bronze BrAZhNMts9-4-4-1, similar by make-up to the bronze BrA9Zh4N4L, used to manufacture ship propellers. The compositions were applied over the plates made of the bronze BrAZhNMts9-4-4-1, the plates were preliminary ground to obtain the values of the roughness parameter Ra of the working surface ranged from 0.5 to 0.9 μm. The stress was measured to break the hardened epoxy coatings off the bronze plate. The results showed that the break-off stress changes with the hardener contents just the opposite way as the epoxy coating acoustic impedance does, and the less completed the process of cross-linking the higher the adhesion of the epoxy coating to the bronze surface. When the hardener content exceeds 9.5-10% by volume the values of adhesion strength and acoustic impedance stop varying: break-off stress takes on a constant minimum value, and acoustic impedance takes on a constant maximum value. In decreasing the hardener content lower than 9.5-10% by volume the adhesion begins to rise. An increase in adhesion is accounted for by an increase in the relative fraction of the epoxy groups with the decrease in hardener concentration. With a decrease in hardener content the scatter of the adhesion values multiplies, the latter is explained by the rise in the epoxy properties sensitivity to hardening conditions with a decrease in the quantity of the hardener.