Influence of Trace Element Additions on Fe Bearing Intermetallic Solidification of a 6063 Al Alloy

摘要

There is an on-going effort to control Fe bearing intermetallic formation during solidification in direct chill (DC) casting of dilute Al alloy billets from recycled material sources, as these insoluble Fe intermetallics control the downstream processing conditions and final properties of the processed products. This paper investigates the influence of molybdenum (Mo) and grain refiner combined additions on Fe bearing intermetallic formation during casting of a 6063 Al alloy. In particular, the grain size and intermetallic phase content of the samples have been characterised using various microscopies and X-ray diffractometry. An intermetallic phase extraction technique has been used to facilitate measurement of the three-dimensional morphology and chemistry of the different Fe intermetallics present, with changes rationalized in terms of the effect of trace additions. Both 'α_c-AlFeSi' and 'β-AlFeSi' are observed in all the castings. After the addition of Al-5Ti-1B grain refiner to the base alloy, β-AlFeSi was predominated in the casting. Further addition of Mo to the grain refined alloy promoted α_c-AlFeSi in the casting. The possible mechanisms for these effects are discussed.