Relation between grain size and coherency parameters in aluminium alloys

Abstract

During equiaxed dendritic solidification, dendritic grains form at the point where primary dendritic crystals become coherent (or impinge on each other). An experimental and theoretical approach to evaluate the grain size in the alloys is proposed, using thermal and constitutional parameters, and the parameters at the dendrite coherency point. For an alloy with a solute concentration below the solid solubility limit, the grain size is inversely proportional to (dT/dt)1/2 Σ miCoi (ki−1) and the coherency parameters (T is the temperature, t is the time, m is the liquid line slope, Co is the original solute concentration, k is the solute distribution, and subscript i is the ith alloying element). For an alloy with a solute concentration above the solid solubility limit, the grain size can be calculated using the dendritic growth interval Σ ki(TLi−Teui), where TL and Teuare the liquidus and eutectic temperatures, respectively, instead of the dendritic restriction factor Σ miCoi (ki−1). For commercial alloys, the grain size can be calculated using the equation of thermal balance in a dendritic grain and the parameters at the dendrite coherency point. The calculations are compared with experimental measurements.MST/3048