Effect of Ce and La on microstructure and properties of a 6xxx series type aluminum alloy

The increase in iron content in secondary sources of aluminum has led to an increase in the amount of Fe-bearing intermetallic phases in Al alloys. One of these intermetallics, beta-AlFeSi, which is seen as the dominant phase in 6xxx series alloys, reduces bendability of wrought alloys, which in turn, limits their usage in the automotive industry. It is known that small additions of Sr prevent the formation of the beta phase and facilitate the precipitation of a less detrimental intermetallic, alpha-AlFeSi, in as-cast alloys. It is worth investigating whether other elements cause a similar effect. Cerium and lanthanum as the least expensive representatives of rare-earth metals are tried as such elements. It is found that in alloys containing 0.1-0.2 wt.% of lanthanum, the fraction of beta particles is pronouncedly less than that in the reference alloy. In addition to this advantage, much smaller grains are seen in the alloy with 0.2 wt.% La. Despite similarities between La and Ce, the latter metal neither modifies the microstructure nor noticeably affects the grain size. Moderate thermo-mechanical processing nullifies the beneficial effect of small La additions resulting in no improvement in the bendability of the alloy.