Primary Dendrite ARM Spacing Effects upon Mechanical Properties of an AL–3Wt%CU–1Wt%LI Alloy

Abstract

The imposition of a wide range of operational conditions in foundry and castings processes generates, as a direct consequence, a diversity of solidification structures. It is well known that mechanical properties depend on solidification structures. The literature presents relationships between yield strength and grain size, such as the Hall-Petch’s equation, or ultimate tensile strength and dendrite arm spacing. In this work, an Al–3wt%Cu–1wt%Li alloy was solidified under upward unsteady state heat flow conditions. Heat was directionally extracted only through a water-cooled bottom made of steel (SAE 1020). The aim of the present study is to obtain correlations between the as-cast microstructure, solidification thermal variables and mechanical properties of an Al–3wt%Cu–1wt%Li alloy casting. The results include tip growth rate (V _L ), cooling rate ($\dot{T}$), primary dendrite arm spacing (λ ₁), ultimate tensile strength (σ _UTS) and yield strength (σ _y) as a function of solidification conditions imposed by the metal/mold system. It is found that the primary dendrite arm spacing decreases with the increase in tip growth rate and cooling rate. In both cases (σ_UTS and σ_y = 0.2 %ε), the finer dendritic arrangement presents superior mechanical properties.