軽金属部材の精密スポット接合技術
■機械金属部 舟木克之 舟田義則 根田崇史
近年，自動車産業等では，鋼部材をアルミニウムやマグネシウム合金等の軽合金に変更し，軽量化する取り組みが活発になってきた。自動車の組み立て用途では，主として重ね合わせスポット溶接が行われているが，電気抵抗の小さな軽合金では抵抗溶融溶接が困難である。一方，スポット摩擦接合(FSJ:FrictionSpotJoining)は，高速で回転する鋼製ツールと母材間の摩擦熱を利用する接合プロセスであり，軟化温度の低い軽合金を対象に研究開発と実用化が急速に進んでいる。しかし，本接合法においては標準化がなされておらず，継手品質の確保や保証に対して不安が残る。そこで本研究では，FSJ継手の接合性を定量的かつ迅速に評価できる非破壊評価法の確立を目的として，厚さ1mm以下のアルミニウム合金薄板をスポット接合する条件を確立するとともに，薄板FSJ継手で生じやすい接合部におけるすきまの成長メカニズム，超音波探傷画像での可視化による接合状態の良否評価を行った。
キーワード: アルミニウム合金，スポット摩擦接合，超音波探傷，金属組織
Study on Fine Spot Joining of Aluminum Alloy Sheets
Katsuyuki FUNAKI, Yoshinori FUNADA and Takashi KONDA
In the automobile industry in recent years, there has been an increasing trend to substitute steel parts for lightweight metals such as aluminum and magnesium alloys. Overlap spot welding is predominantly used in the automobile assembly process, but molten welding of lightweight alloys is difficult because of their low electrical resistance. On the other hand, friction spot joining (FSJ) is a non-melting joining process using a high-speed rotating steel tool and frictional heat between the tool shoulder and the material's surface. Research on FSJ with regard to lightweight alloys that have low softening temperatures has been rapidly advancing to the practical stage. However, with no standardization in this joining method, there is still some anxiety with regard to security and guaranteeing of joint quality. In this study, for the purpose of establishing joint quality guidelines consisting of quantitative and rapid assessment of the characteristics of spot friction joined parts, we validated the utility of the spot joining condition of Al alloy sheets with a thickness of 1 mm or less. We also examined the widening mechanism of the joint gap between tin sheets that tends to form during FSJ processing, and carried out an evaluation by means of an ultrasound image.
Keywords : aluminum alloy, friction spot joining, ultrasonic inspection, metal structure
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