Furukawa-Sky Review No.7 (April 2011)

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Material Properties and Sheet Metal Forming of Aluminum Alloys

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  • 上野 洋一
    Yoichi Ueno
  • 小山 克己
    Katsumi Koyama

本稿では,缶材や自動車ボディーシートの成形加工に使用される3000(Al-Mn)系合金,5000 (Al-Mg)系合金および6000(Al-Mg-Si)系合金の特徴や成形加工の現状について紹介する。
Al-Mn系合金が使用されるキャンボディ材の深絞り(drawing)工程では集合組織制御による耳の発生防止が,しごき(ironing)工程ではMn 系金属間化合物がダイスに凝着したアルミニウム粉を除去し,缶表面光沢低下防止が図られている。Al-Mg 系合金が使用されるキャンエンドでは,高加工部分であるカウンターシンク部の成形時の割れや2 次バックリングによる亀裂の発生の抑制策が取られている。

The 3000-series (Al-Mn), 5000-series (Al-Mg), and 6000-series (Al-Mg-Si) aluminum alloys are applied to can stocks and automotive body sheets. The material properties of these aluminum alloy sheets and the present situations of sheet metal forming will be presented in this paper. In the drawing process of can body stocks for which Al-Mn alloys are used, the textures are controlled in order to suppress earing. And, in the ironing process, Mn-based intermetallic compounds prevent the built-up of aluminum flakes on the ironing die, avoiding the galling on can body surfaces. In the can ends in which Al-Mg alloys are used, various countermeasures are implemented to prevent cracking at the countersink part which is strongly deformed, and also to suppress cracks at buckling.
In the hemming process of automotive body outer panels in which Al-Mg-Si alloys are used, cracks on the surface of the hemming ridgelines are suppressed by reducing the number of coarse-sized second-phase particles. And in large stretch forming, crystal orientation is controlled in order to prevent ridging (i.e., surface defects).
To improve the deep drawability of aluminum alloy sheets, texture control by asymmetric warm rolling has been studied. Also, the high temperature blow forming technology using high ductility that appears at elevated temperatures has been put into practical use. Additionally, helped by the application of servo press and lubricant coating to die faces, the usage of aluminum alloy sheets to complex deep-drawn components is expected to increase.

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