Hot-Dip Al-Zn Alloys Coating On TC4 Surface To Prevent Titanium/Aluminum Alloys Galvanic Corrosion

Because of the good integrated mechanical properties, low density and high strength to weight ratio, titanium alloys have been widely used in the filed of aerospace and spaceflight. But when the titanium alloys contact with aluminium alloys in corrosion solutions, there will be a problem. The problem is contact corrosion which occurred by the large difference of stability potential between titanium alloys and aluminium alloys. Because of the promotion effect of stress and crevice, the contact corrosion problem will be more serious when the titanium alloy fastener is used to fasten the aluminium alloys.According to the problem, this article will start with resolve the main factor of the causations. The measure is to form a coating of Al-Zn on titanium alloys by hot-dip technology to decrease the potential difference of the contact metals to weaken the effect from galvanic corrosion. Then, designed appropriate electrochemical corrosion test, immersing corrosion test and the neutral salt-mist experimentation to test the protection effects of the Al-Zn coating on the titanium alloy. At last, the structure morphology, composition, and phase composition of the coating were analysised by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), the effect of the contact corrsion protection was also been tested by these modern methods.The results showed that: 670℃, immersing 7min, 0.1m/s out speed, add 0.2wt% of Ce is the best processing parameter for the two-bath single solvent hot-dip processing. Under the processing parameter, the coating has the best contact corrosion protection and the mechanical property of the coating can content with the contact use also. The thickness of the modified layer can reach 40μm. The layer section structure was formed by outermost layer which is rich of Al-Zn phase and middle layer which is rich of Ti-Al phase. Not only decreased the stability potential of the titanium surface but also provided protection to the cathodic metal. And the layer has compact structure, high surface hardness, good adhesion, suitable for the use of contact fastenners; the result of electrochemical corrosion test, immersing corrosion test, and the neutral salt-mist experimentation show that: the layer can give good protection to the Ti/Al alloys contact corrosion. At least it can increase the service life of aluminum alloys for 2~3 times. The coating has a protective effect to the titanium alloy substrate, and also has a certain resistance to corrosion itself.