High-speed twin-roll strip casting of Al-Mg-Si alloys with high iron content

Thin strips of the 6063 aluminum alloy and the alloys with increased nominal Fe contents (0.7-6 mass%Fe) were fabricated directly from the molten alloys using a vertical-type high speed twin-roll strip caster equipped with a pair of water-cooled pure copper rolls. The estimated cooling rates from the DAS measurement were about 4500 and 100 degrees C/s at the near the surface region and the mid-thickness region of the strip respectively. Refinement of Al-Fe-Si intermetallic compound particles was also successfully achieved, however, segregated coarse particles were also observed at the mid-thickness region. The cast strips were cold-rolled and heat-treated to form 0.5 mm-thick thin sheets. They were either naturally aged at room temperature (T4) or artificially aged (T6), and then subjected to bending, tensile and hardness tests. No detrimental effect of Fe was appeared concerning the bendability even in the alloy containing 3 mass%Fe. No cracking took place even in the 180 degrees bending (hemming) test. The reduction of age-hardenability was evident for the alloy with 1 mass%Fe and more. The alloy sheet containing 0.7 mass%Fe exhibited not only a good bendability in the T4 condition but also the larger proof stress and UTS than those of the master alloy in the T6 condition. This means that the capacity of Fe impurity in a 6063 alloy (0.35 mass% according to JIS) can be doubled by using the present roll caster. Strip casting at a high cooling rate using the present roll caster is considered to be a promising method for reducing the detrimental effect of impurity iron from the scrap melt.