The influences of magnesium on the mechanical properites of Al-Mg alloys were investigated. The tensile strength increases with magnesium up to 6%, and the elongation and the impact resistance decrease as rapidly as magnesium increases. The effect of heat-treatment on Al-Mg alloys and the influence of the structure of the casting before treatment on its properties after treatment are described.
The solution treatment consisted of a preliminary soaking for 0.5 or 24 hrs. at 420° followed by precipitation at 100_??_300° for 2_??_10 hrs. In the case of solution treatment, the hardness does not increase, but when the precipitation treatment were carried out, they show a marked increase of hardness. An appreciable amount of precipitation hardening is possible in alloys containing 8% or more magnesium. In any alloy, the maximum hardness is obtained by tempering at about 175°
The corrosion resistance in sea-water shows the maximum resistivity at 6% magnesium in cast or heat-treated condition. In case of thse alloys for which the solution treatment is for 3 hrs. at 420° followed by air cooling, the effect is more beneficial than water quenching, while in tempering the alloys of these series the corrosive resistance is recduced.
The mechanical properties of some of the more important Al-Mg alloys “Hydronalium” in the extruded condition, which contained 6_??_8% magnesium and 0.3_??_0.5% manganese, have been investigated. The mechanical properties of Hydronalium is barely affected by quenching up to 420°. But above 420°, the effect of temperatures is to decrease the mechanical properties markedly. When the extruded bars were quenched in water or air at 420° for 0.5_??_10 hrs., the heating time has a marked effect to improve the elongation up to 5_??_7 hrs. But after tempering the mechanical properties decrease as the tempering temperature increases.
Corrosion of Hydronalium in salt water was also investigated. In the case of quenching, it does not appreciably affect the corrssion resistance up to 420°. Above 420°, however, the corodibility is remarkably improved in air cooling, but in water quenching, the resistivity decreases progressively with the increase of quenching temperature. In the case of tempering, Hydronalium are more corrodible than in any other state.
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