Recently, demand for environment protection and reduction of energy consumption has led to active development of technology to reduce the weight of transportation devices. Furthermore, due to the development of the ocean leisure industry, there is a increasing number of small shipbuilding including yacht using aluminum. However, there are a lot of problems to be solved in aluminum ship welding from the technological, economic and environmental perspectives. An alternative to solve these problems is the friction stir welding technique. But, inflow frictional heat is generated in case of friction stir welding of 6061-T6 alloy, and the crystalline structure grows, resulting in weak mechanical strength. Accordingly, this study is to improve the mechanical characteristics and corrosion resistance of FSWed 6061-T6 alloy through annealing heat treatment. This study compared the characteristics with time of heat treatment at a constant temperature for the annealing heat treatment. Results of electrochemical experiments, the stir zone in annealing time 60min. showed the low corrosion current density. Micro-Vickers hardness in 60min. presents the higher value than the other conditions.

The sustainable development of engineering, mechanical instrument requires higher speed and higher power. It cause a physical damage is excessive damage for underwater rotating system as cavitations and erosion, but also electrochemical corrosion by chloride ion and flow of current in marine environment. In this study, we assessed electrochemical corrosion characteristics of aluminum-bronze that are the material for the underwater rotating system used in the ocean industry and studied the complex behavior of electrochemical corrosion and cavitation corrosion through the hybrid test that also included cavitation corrosion environment. After the cavitation hybrid tests, surface of specimens are observed to measurement damage degree using 3D optical microscope and compared the average of damage depth by immersion time. The observation of the surface micro-structure suggested that the corrosion took place initially in β phase that has poor corrosion resistance in spite of high hardness.