Study on the galvanic corrosion of Ti-Al joints with different bolting assembly methods

Abstract

Two lightweight metals of Ti and Al alloys are widely applied in the aerospace industry, which are inevitably connected as Ti-Al joints in practical applications. The assembly method significantly influences the galvanic corrosion behavior of Ti-Al joints. The galvanic corrosion rate and “effect distance” of TC18 Ti alloy and 20,250 Al alloy joints assembled with the bolts of 304 stainless steel and H62 brass were investigated by electrochemical tests, finite element modelling (FEM), and neutral salt spray validation. The results indicate that the corrosion rate of the anode 2050 Al alloy increases by approximately 50 % when H62 brass bolts are employed compared to 304 stainless steel bolts. This phenomenon is attributed to the improvement of passivation film on the cathode 304 stainless steel during the galvanic corrosion process, which inhibits the charge transfer to reduce the acceleration effect. Due to the effect of solution resistance, the “effect distance” of galvanic corrosion is only approximately 5 mm. The corrosion of 2050 Al alloy around the bolts is mainly accelerated by the bolts instead of TC18, whereas other contact regions within the “effect distance” range, the TC18 Ti alloy plays a main role, and the acceleration effect is mainly determined by the cathode/anode area ratios of Ti and Al.