By applying a controlled amount of gallium (3 mg or 5 mg) to double-notched samples, the effects of the gallium on the grain boundary chemistry and tensile properties of AA6061-T4 alloy were investigated. Commercial-purity aluminum AA1050 was used for comparison to determine whether alloying elements would correlate with Ga-induced embrittlement and to elucidate the physical reason that governed the occurrence of intergranular fracture in the AA6061 Al-Mg-Si alloy. The AA6061 and AA1050 samples wetted by 3 mg or 5 mg of Ga were held statically for 7 days before tensile tests were conducted. The 6061 Al-Mg-Si samples with gallium were fractured intergranularly. However, the Ga-treated AA1050 samples had a mixed fracture mode, showing better strength and ductility than the Ga-treated AA6061 alloy, independent of whether the samples had their longitudinal axis parallel or perpendicular to the rolling direction, or the holding temperatures before tensile tests. Auger electron spectroscopy scanning the intergranular facets on fracture surfaces showed that the Auger peak-to-peak ratio I-Ga/I-Al of 6061 samples was similar to that of 1050 samples, but the high intensity of Mg signal was detected from the intergranular fracture surface of the AA6061 alloy. Magnesium being induced by Ga to enrich on the grain boundary and free surface of the AA6061 alloy was confirmed. The intergranular embrittlement of the 6061 T4 Al-Mg-Si alloy wetted by small amount of Ga involves the combination of the following two effects: Ga metal on grain boundary embrittlement, and Ga-induced magnesium enrichment on grain boundary that further decreases the strength of the grain boundary
This investigation examines the grain boundary segregation of Mg and Si in AA6061-T4 alloy, using Auger electron spectroscopy technology. Liquid metal embrittlement by gallium was conducted to fracture the AA6061-T4 alloy intergranularly to obtain compositional information directly from the grain boundary facets. The amount of liquid gallium applied is controlled to break the alloy intergranularly at room temperature, importantly without Ga-bearing particles or a film covering the fracture surface. The method of generating a fully intergranular fracture surface for AA6061 is elucidated. The AES analysis reveals that Mg in 6061 T4 alloy is segregated at grain boundaries, but Si does not. The segregation of Mg depends on the rolling direction. The mean peak-to-peak ratio I Mg =I Al of the specimen whose longitudinal axis is perpendicular to the rolling direction is about three times that of the specimen whose axis parallel thereto. The grain boundary segregation is not result oxidation-induced; surface segregation also makes no contribution.
This study reports a simplified method to grow CuAlO2 crystals of submillimeter sizes with a highly anisotropic
shape
of a platelet. The solid-state reaction of forming CuAlO2 at ca. 1373 K in the first stage of the conventional flux method
is no longer required. The CuAlO2 platelets nucleated directly
onto the (0001)sapphire surface in a melt of Cu2O saturated with Al2O3 at 1473 K. The excess
flux was mostly removed by the capped alumina plate on cooling with
a limited amount of residue which can be leached afterward. The CuAlO2 platelets all have a 3R crystal structure with no line and
planar defects observed by TEM. The CuAlO2 crystals emit
a luminescence at 3.49 eV associated with resonant Raman effect resulted
from a band-to-band transition in room-temperature PL measurement.
The facile fabrication method for growing highly anisotropic CuAlO2 crystals paves the way for their practical application in
photoelectrochemical devices.
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