Laser Rapid Solidification Microstructure in Single Crystals of Al and Al-2% Cu Alloys(Materials, Metallugy & Weldability)

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Characteristics of rapid solidification were investigated in detail in terms of microstructure, solidification modes, growth crystallography and microsegregation by irradiating a pulsed Nd: YAG laser on the specific surfaces (001) (011) and (111) of single crystals of pure Al and Al-2%Cu alloys. In laser spot weld fusion zones of both alloys, epitaxial growth occurred as planar interface and then cellular or cellular dendritic interface from the unmelted semi-spherical base metal inwards. Also a number of grains were formed as "stray" crystals in the upper part of shallow fusion zones and in central part of deep fusion zones in Al-2%Cu alloy. In pure Al, cells had the same crystallographic orientation as the base metal. However, in Al-2% Cu, the crystallographic orientations of cells were several degrees different from those of the base metal. The growth direction of cell trunks in pure Al was gradually shifted from the <100> direction toward the directions of heat and liquid flow. In Al-2%Cu, on the other hand, dendritic cell trunks grew straight, which were deviated up to 15° at the maximum from the <100> to heat flux flow direction immediately after the growth initiation. Moreover, net-like (weave) microstructure of cellular dendrites was observed in boundary zones where cells of different <100> growth directions impinged. Cu element was likely to segregate at grain and cellular dendritic boundaries, resulting in the formation of Cu-enriched intermetallic phase. It was also confirmed that cracks took place at grain boundaries but not at cellular dendritic boundaries.
大阪大学の論文

Laser Rapid Solidification Microstructure in Single Crystals of Al and Al-2% Cu Alloys(Materials, Metallugy & Weldability)

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