Gallium-induced magnesium enrichment on grain boundary and the gallium effect on degradation of tensile properties of aluminum alloys

Abstract

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

Atomic-scale analysis of liquid-gallium embrittlement of aluminum grain boundaries

“…However, recent nanoscale experimental studies suggest that one of the primary contributing factors in LME is the formation of intermetallic compounds at GBs [1] and bilayer interfacial phases (e.g., in Ni-Bi) [17]. The lack of a definitive understanding of the mechanistic origin of LME hinders our ability to satisfactorily address LME in important technologies, including in the nuclear-power generation sector, where liquid-metal coolants are in contact with metallic structural components, and in industrial sectors that employ liquid-based joining technologies (e.g., soldering and brazing) [4,9,10,16,19,32].…”

“…Liquid-metal embrittlement (LME) is a phenomenon experienced by many intrinsically ductile metals, including aluminum (Al), nickel (Ni), and copper (Cu). These metals exhibit a drastic loss of ductility in the presence of certain liquid-metals, such as gallium (Ga), bismuth (Bi), and mercury (Hg) [1][2][3][4][5][6][7][8][9][10]. Understanding the mechanisms behind LME has been of particular interest in both experimental [2,3,5,8,[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] and simulation [7,9,[26][27][28][29][30][31][32][33] research.…”

Surface free energy and surface stress as elastic components of the surface tension of condensed matter

“…These authors deduced the surface stress of small gold parti cles by measuring the reduction of the lattice constant versus the radii of the particles". Nowadays there are hundreds of thousands of experimental and theoretical works considering this effect and dependences of many physico mechanical properties including the complicated connection of the elasticity modulus with the nanoparticle radius, electrolyte composition and the electrode potential, see table, S3 and [34][35][36][37][38][39][40][41][42][43][44][45][46][47]. These works provide a clear proof of the natural con nection between the elastic potential energy (surface energy) and interatomic bonds.…”

“…In high vacuum (as the reference state), there are no external effects and the elastic surface energy is the only and natural energy source leading to surface stress, elastic strain and the lattice contraction (see above), changing the elasticity modulus and to other nano effects [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. Most of these effects have been theoretically explained using the purely elastic lattice respond to both the surface energy and the surface stress.…”

Ductile-to-brittle transition for the aluminum alloy contacting to liquid gallium metal

“…Nevertheless, the effect of a critical amount of liquid metal on the fracture behavior of a solid metal has been ignored in most LME studies. In the authors' previous paper [10], various amounts of Ga (3 mg and 5 mg) were applied on the AA6061 alloy at 25 • C for 7 days. The experimental results revealed complete intergranular fracture of all samples.…”