Effects of Cooling Rate on the Properties of High-Manganese-Aluminium Bronze

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  • 高マンガン・アルミニウム青銅に対する諸性質と冷却速度について
  • コウマンガン アルミニウム セイドウ ニ タイスル ショ セイシツ ト レイキャク ソクド ニ ツイテ

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Abstract

In our previous report (Effect of Nickel, Iron and Manganese Addition on β→α+γ2 Transformation of Cu-Al Alloys), adding Mn to Al-bronze containing β phase was effective to stabilize β phase and depress the so-called self-annealing phenomenon. Based on that result, this experiment was carried out to decide the region free from γ2-precipitate which caused self-annealing in Cu-Al-Mn system. The microstructures and hardness of Cu-Al-Mn alloys containing 5∼12%Al and 4∼12%Mn, water quenched or treated at various cooling rate as 1, 0.15 and 0.02°C/min, was examined and noted in diagrams. Then the mechanical tests of Cu-9.5%Al-Mn and Cu 8%Al-Mn alloy castings containing various Mn amount were carried out on tensile strength, elongation and impact-value. The results obtained are summarized in the following: The microstructures of high Mn-Al-bronzes containing above 6 wt%Mn consist of α,β and Cu3Mn2Al phases and free from the precipitation of γ2 and it was suggested they show excellent mechanical properties even when slowly cooled, say, at 0.02°C/min.In the results of mechanical test, Cu-Al-Mn alloy containing β phase showed an increase of tensile strength and a slight decrease of elongation with the increase in Mn wt%, but did not show self-annealing when containing high Mn content.

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