Al-Mg系合金の研究(第2報)

Abstract

Adding 0.5 to 10% Si to Al-Mg (2, 4, 7 and 10%) alloys, I have investigated its effect on the mechanical properties, age-hardenings and corrosibilities. The results obtained may be summarized as follows:- (1) Si has a marked effect in the tensile strength, which improves with the addition of Si till Mg content is up to 4%. While if Mg content is over 7_??_10%, the addition of Si remarkably increases the tensile strength up to 3_??_4%. On the contrary, the elongation and impact resistance decrease rapidly with the Si addition up to 3%, and after that the decrease is gradual. Though the Brinell hardness increases as rapidly as the Si content does, the influence of Mg does not show any significant change. (2) Whether air or furnace cooling is applied, the hardness decreases as the annealing temperature elevates. Mg has a pronounced effect to increase the hardness of these alloys when Si content is small. If Si content is over 7%, however, the increased hardness due to Mg addition is not so marked as that of small addition of Si. (3) Though the hardness increases with increase in quenching temperature, it is rather small. The influence of the addition of Mg and Si on the hardness also shows the same tendency as that in an annealed state. (4) The additon of Si to Al-Mg alloys give a coinsiderable influence upon the artificial age-hardening, and that the ageing phenomenon of the alloys containing more Mg than the ratio Mg2Si is somewhat different from the alloys containing more Si than the same ratio. The alloys containing more Mg than this ratio show less age-hardening, and the maximum hardness in these alloys is obtained by tempering at 175°. (5) The effect of Mg and Si on the “Ruckbildung” phenomenon is not so marked as that of Al-Cu alloy or Duralumin. A small addition of Si to these alloys has no essential effect on the hardening, but the hardness increases with increasing Si content. (6) The corrosion resistance in HCl, NaOH or 3% NaCl+l% HCl solution in the cast state shows a deleterious effect, and especially in HCl solution they are more severely corroded than the others. Tests on these alloys indicate that the addition of Si has a marked effect in improving the corrosion resistance up to 4_??_7% Si, while the addition of Mg is markedly harmful as Mg content increases. (7) The effect of tempering on the corrosibility in sea-water was practically nil up to 300° Being tempered, they have more excellent resistivity against corrosion than that of quenching state. The effect of Si addition also gives the best corrosion resistance up to 7% Si, but addition of Mg tends to lower slightly its resistant quality.