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Vol.38, No.5, 693 ~ 699, 2000

Title

Pesearch Paper / Powder Matallurgy : Fabrication of Splat - quenched Al 7075-Mn Extrusions and Effect of Manganese on the Aging Behavior

정연수Youn Su Jang,임수근Su Gun Lim

Abstract

Rapidly solidified flakes of 7075 aluminum alloys with the addition of 0.5-2.5 wt.%Mn were fabricated by atomizing the alloy and subsequently splat quenched on a rotating water-cooled copper drum. Consolidation of these flakes was done by cold pressing, degassing and hot extrusion at a reduction ratio of 25 to 1. A typical flake was approximately 10 ㎜ in diameter, and its thickness is about 25 ㎛ at center and increased near the edge. Effect of manganese on the aging behavior was examined by DSC(differential scanning calorimetry) and TEM(Transmission electron microscopy). The aging heat treatment of the extrusions investigated the solution treatment at 490℃ during two hours followed by the aging at 120℃ and the peak hardness time showed at 1300 minute. The cooling rate of the apparatus was estimated as 1.8×10^6∼5.5×10^6℃/sec from the measurement of interlamellar spacing Al-33 wt.%Cu eutectic alloy. The microstructure of splat quenched flakes showed microscopic α-Al phase and eutectic compounds. Microhardness of flakes increased with the addition of manganese due to fine particle of their eutectic compounds. P/M materials also containes fine dispersion of eutectic compounds and showed higher hardness even after annealed at high temperatures. P/M materials showed higher hardness at T6. However, addition of manganese appreciable reduced the age hardening of 7075 alloy. As results of observing the microstructure of Mn added extrusions, the dispersoid of fine Mn compounds(Al_(24)Mn_5Zn) which have 0.2 ㎛ or less than it were observed and also these Mn compounds made the Precipitation(η`(MgZn₂)) quantity lower.

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