P. Merle

Precipitation effects on thermopower in Al-Cu alloys

Abstract The precipitation influence on the thermoelectric power (TEP) of Al-Cu alloys (with from 2 up to 5 wt% Cu) has been observed. It has been shown that incoherent θ precipitates have no influence on TEP, in agreement with previous observations in various metallic alloys where similar precipitates form. On the opposite metastable plate-like precipitates (GP zones, θ″, θ′) induce a contribution to TEP, which is the larger the higher the measuring temperature; furthermore a correlation between the sign of this contribution and the nature of the stresses induced by the particles is observed.

Coarsening of θ′ plates in Al-Cu alloys—II. influence of ledge mechanism

Abstract A theoretical study was made of the two coarsening mechanisms of θ′ plates: 1. morphological evolution and 2. coarsening at constant aspect ratio. In both of them ledge migration on the broad face of precipitates is found to be the controlling process. The analysis of the first mechanism leads to an evaluation of the mean diffusion coefficient of copper in the θ′-matrix interface. For the second mechanism, the hypothesis of an heterogeneous nucleation of ledges due to the impingement of precipitates leads to a linear theoretical relation between the mean diameter D and t 2 11 . This relation agrees rather well with the experimental results.

Experimental and theoretical determinations of the yield stress of an alloy containing plate-like precipitates: θ′ phase in an Al-4wt.%Cu alloy

Abstract The evolution of the yield stress of an Al-4wt.%Cu alloy was studied during the stage in which the precipitates became coarser. The correlation between the yield stress and the thickness of precipitates allows us, in spite of the existence of three different orientations of precipitates in the matrix, to represent the precipitate configuration by a parallel-plate model. Using this model, good agreement is found between the experimental and theoretical values of the yield stress.

Consolidation d'un alliage d'aluminium à 4% en poids de cuivre à l'Etat θ′. Relation entre limite elastique et dureté

Different ageing treatments have been used to produce θ′ precipitates in an AlCu 4 wt.% alloy. The tensile stress-strain curves which were obtained from the various states can be described by the equation σ = RE + Aϵm, where A and m are constants, the rate of work hardening being independent of the size and distribution of θ′ precipitates. Furthermore, a linear correlation between the conventional flow-stress RE and the Vickers hardness HV can be established. The same type of relation is also observed for the intrinsic contribution of θ′ precipitates to these two values.

Study of the dissolution kinetics of the θ phase in AlCu alloys using thermoelectric power measurements

Abstract A comparative study of the dissolution kinetics of θ precipitates in an AlCu alloy was made using classical methods (hardness, scanning electron microscopy and differential scanning calorimetry) and thermoelectric power (TEP) measurements. It is shown that TEP measurements are the most suitable method. The advantages and limitations of this method are given.

Validity of a Lamellar Model for Yield Stress Variation of Alloy Containing Plate-like Precipitates

ABSTRACT The variation of yield stress of an Al-4 wt % Cu alloy during coalescence of θ′ plates is studied together with the geometrical parameters of precipitation. Different models of repartition for θ′ precipitates are investigated to explain these variations. The correlation between the evolution of yield stress and the thickness of 0′ plates leads to consider lamellar models.