Spatiotemporal aspects of the Portevin–Le Chatelier effect in annealed and solution-treated aluminum alloys

By employing the dynamic digital speckle pattern interferometry technique, spatiotemporal aspects of the Portevin–Le Chatelier (PLC) effect in both annealed and solution-treated Al–4%Cu alloys are investigated. The effect of dynamic strain aging is enhanced in response to increased solute concentration in solution-treated materials. Influence of aging on the critical strain of the PLC effect is also reported.     

Le rǒle de l'adsorption dans les réactions superficielles des gaz sur les métaux

The role of adsorption in connection with surface reactions of gasses on metals During the reaction between a metal and a gaseous mixture of hydrogen and hydrogen sulfide a tridimensional surface layer of metal sulfide is formed progressively, provided the hydrogen sulfide partial pressure exceeds the equilibrium pressure corresponding to the reversible dissociation of the sulfide. When the partial pressure is below this equilibrium pressure there is no reaction but only adsorption with formation of two-dimensional compounds, while the crystal orientation of the surface gives rise to a certain selectivity. The surface energy of the different crystal faces undergoes in that various modifications, so that the mobility of metal ions in the surface is modified and differences in self-diffusion occur. These phenomena may have certain consequences with regard to the progress of the reaction (nucleation and epitactic relations). An extension of the theory to media other than sulfur appears feasible.     

铝合金变极性等离子弧焊接的工况适应性

为克服厚板铝合金穿孔焊接熔池极易失稳的难题,该研究从厚板焊接时电弧温度场出发,旨在探究厚板穿孔焊接熔池稳定性的机理。通过建立三维数值模型,研究了焊接母材厚度分别为5 mm和16 mm下变极性等离子电弧的温度场、流场和电流密度分布。结果表明,随着板厚的增加,变极性等离子电弧温度场分布发生改变,5 mm板厚电弧温度的衰减情况为线性,而16 mm厚板焊接的电弧温度衰减情况为二次型,使得温度变化更加复杂。变极性等离子弧焊接5 mm厚度铝合金时,整个小孔熔池的电流密度呈1.0 × 10⁶ A/m²以上,但是在焊接16 mm厚板铝合金时,相同电流密度仅达到小孔深度的12 mm处。该研究有望对实现大厚度铝合金稳定焊接,拓宽变极性等离子弧焊接应用范围提供理论指导。