Michihide Yoshino

Corrosion Behavior of Alloy A3003 After Brazing in HCl, CH3COOH, and Mixed Solutions

Dip and dry corrosion tests were carried out on Alloy A3003 (UNS A93003) using hydrochloric acid (HCl), acetic acid (CH3COOH), and a mixed solution. After 50 corrosion test cycles with the HCl solution, pitting corrosion occurred in some parts at higher concentrations, but corrosion weight loss was very low. In the case of the CH3COOH solution, general corrosion occurred, thickness decreased, and weight loss significantly increased as the concentration grew. In the case of the mixed solution, both general corrosion and pitting corrosion occurred, and corrosion mass loss increased as the HCl concentration grew. Also, in concentrations of more than 50 ppm of HCl, the number of pits significantly increased. Electrochemical polarization measurements were done to understand the corrosion forms for each acid. In the electrochemical polarization, the pitting potential became less noble with increasing concentration of HCl. No distinct effect of CH3COOH on the pitting potential was confirmed, but corrosion curren...

Intergranular Corrosion Mechanism of Brazed Al-Mn-Cu-Si Alloy

This paper investigated the effect of Si addition on intergranular corrosion susceptibility for brazed Al–Mn–Cu alloy. Water-quenched samples have no intergranular corrosion (IGC) susceptibility, however, slowly cooled samples have IGC susceptibility. This implies that IGC susceptibility was caused by precipitation during cooling. In addition, IGC susceptibility depends on Si content. Low Si additive alloy has high IGC susceptibility. This is because the Mn/Cu depleted zone is formed near the grain boundary due to preferential precipitation of Mn-bearing compound and CuAl2 on the grain boundary. Conversely, optimum Si addition inhibits IGC due to the absence of preferential precipitation on the grain boundary. The excess Si alloy has high IGC susceptibility as the Si depleted zone is formed around the grain boundary due to the preferential precipitation of coarse Si particles on the grain boundary.

Recrystallization Behavior of Twin-Roll Cast 3xxx Series Aluminum Alloy

Twin roll casting (TRC) is an efficient process used to produce thin plates directly from molten metal. However, TRC has a much higher cooling rate during solidification compared with conventional direct chill casting. Accordingly, the constituent phases are refined and the added elements are supersaturated by this casting method. Supersaturation of the added elements hinders both recovery and recrystallization because fine dispersoids precipitate from the supersaturated solid solution during annealing [ and coarsen the grain size of the final plate, which leads to degradation of formability. Therefore, it is important to understand the influence of the solute element and dispersoids on recrystallization behavior to obtain an appropriate grain structure for forming. In this study, the effects of the homogenization conditions and cold rolling reduction on the recrystallization behavior of twin-roll cast 3XXX series aluminum alloy were investigated.

Effect of Additional Elements of Al-Si Filler Alloy on Flowability and Clearance Fillability

Aluminum alloys are widely used for automotive heat exchangers manufactured by brazing processes. All joint gaps must be filled with Al-Si filler metal to prevent the leak of refrigerant. Recently, brazing of heat exchanger components has become difficult due to the decrease in the thickness of the brazing sheets. Since the fluidity of Al-Si molten metal is very high, the flow of molten filler metal sometimes causes dissolution of the base metal or defect of joints. In this study, we investigated the effect of additional elements (such as Mn, Fe, Ti and Zr) of Al-Si filler metal on the flowability and clearance fillability using our original evaluation model. The results indicated that the addition of Mn or Ti improved the clearance fillability significantly. We clarified the mechanism that additional elements change the properties of molten filler metal, by measuring the viscosity of each filler metal and observing the solidified microstructure.