Corrosion And Protection Of Al-Si Alloy And Its Weldment

Al-Si alloy is one of important aluminium alloys in automotive. It has many advantages of low density, optional weight to strength ratio and good dimensional stability. Al-Si alloy was corroded severely in the corrosion environment. Currently, the main composition of a conventional coolant is 30-70 vol% ethylene glycols. The corrosion of Al-Si alloy in the coolant shortens the service life of the automotive engine. The protection of Al-Si alloys has been a subject of remarkable technological importance.In this paper, fluorescent spectra, weight-loss method, electrochemical measurements were used to study the corrosion behavior of AA6061 alloy in simulated atmosphere and motor coolant. The protection by some corrosion inhibitions also has been investigated. The results were as follows:(1) The corrosion of AA6061 alloys in stimulate salt fog was monitored by fluoreacence proble technology. The fluorescence can indicate the evolution of local corrosion. The electrochemical noise analysis was used to study the corrosion process of Al-Si ally in 3% NaCl solution.(2) A strengthening of cathodic depolarization was adopted. Electroche- mical analysis methods and surface analysis techniques were used to study the corrosion behaviour of hybrid welded AA6061 aluminium alloy. Nd:YAG laser-gas metal arc (GMA) hybrid welding enhances the corrosion susceptibility of AA6061 alloy. The hybrid welding leads to the dendritic segregations of precipitate phase in the weld fusion zone (WFZ). Severe pitting and a thick porous surface film were observed in the WFZ, which is due to the increasing of the galvanic corrosion couplings by the increased precipitate phase.(3) The corrosion behavior of AA6061 alloy was investigated in ethylene glycol-water. The results suggested that there were two corrosion periods. The corrosion rate in the first corrosion process is lower, while it is higher in the second corrosion process. In the earlier stage, the advantage of ethylene glycol inhibited the corrosion of the AA6061 alloy. However, with the increasing immersion time, ethylene glycol accelerated the corrosion of AA6061 alloy. The additive of glycollic acid enhanced the corrosion susceptivity of AA6061 alloy in the coolant.(4) The inhibition of some inorganic and organic compounds for AA6061 alloy was investigated. The results showed that sodium silicate and sodium benzoate had better protection effect for AA6061 alloy. At 25℃, sodium silicate acted as anodic inhibitor, while it was a cathodic inhibitor at 88℃. Dicarbosylic acids (Succinic acid, Adipic acid and Sebacic acid) were tested as the novel corrosion inhibitors for Al-Si alloy. It is showed that dicarbosylic acids act as anodic corrosion and can form an insoluble protective film on the alloy surface.