Influence of solid-solution treatment on corrosion performance of cast AM50 magnesium alloy
It was investigated by quenching the AM50 magnesium alloy test samples in water after T4 treating (420 °C) for 24 h. Then both kinds of the test bars were immersed in 3.5 wt. % NaCl saturation Mg (OH) 2 aqueous solution for 0, 24 and 72 h. Then tensile tests were taken. The microstructure of the samples was analyzed by scanning electronic microscope and X-ray diffraction. The results show that though solid-solution treatment improved the corrosion residual strength of the cast AM50 magnesium alloy for 24h, the deeper corrosion pits developed on the heat-treatment samples on 72h caused more drop of the strength compare to the untreated samples. The solid-solution treatment and the extreme depth theoretical of corrosion pits effect together to the corrosion residual strength.
Effect of T6 heat treatment on corrosion resistance and mechanical properties of AM50 magnesium alloy
Abstract To improve the corrosion resistance and mechanical properties of AM50 magnesium alloy, T6 heat treatment was applied. The microstructure, mechanical properties and corrosion properties of as-cast and T6 heat-treated alloy were studied. The results indicated that the β phase presented at the grain boundaries along with Al–Mn phase after T6 heat-treatment. Because of solid solution and aging treatments, the tensile strength of the AM50 magnesium alloy was increased. The decreasing of the β phase owing to the solidsolution during T6 treatment, which causes Al solid solution in the α-Mg phase, and it is favourable for increasing the corrosion resistance of AM50 magnesium alloy. The fracture mechanisms of the as-cast and T6 heat-treated alloy were quasi-cleavage fracture. The corrosion residual strength of the T6 heat-treated alloy was higher than that of the as-cast alloy. Compared with the as-cast alloy, the corrosion rate of the T6 heat-treated alloy decreased gradually.
Phase formation during mechanical alloying in the Ti–Si system
Abstract Mechanical alloying of Ti–Si powder mixture or TiH 1.924 –Si powder mixture was performed by high-energy ball milling, in which the Ti to Si mole ratio was 1:2. The phase formations in both mixtures during milling were investigated by X-ray diffraction. Mechanical alloying a mixture of elemental powders led to the formation of TiSi 2 equilibrium compound, while when starting from Si + TiH 1.924 , a metastable phase was formed. The metastable phase completely transforms to TiSi 2 when the mechanically alloyed powder is annealed at temperatures above 800 °C. Two different pathways of phase transitions during mechanical alloying are attributed to the existence of hydrogen atoms, i.e., when starting from Si + TiH 1.924 compared to Si + Ti, the kinetics for the formation of the TiSi 2 intermetallic compound slows down. The kinetics related to the different phase transitions depending on the starting powder mixture are discussed.