Homogenization of EN AW 6005A Alloy for Improved Extrudability

The homogenization practice for EN AW 6005A was investigated. It requires an 8-hour soaking at 853 K (580 degrees C) to even out the Mg and Si distribution in the aluminum matrix and to fully transform the monoclinic beta-Al5FeSi plates into relatively small round alpha(c)-Al-12(Fe,Mn)(3)Si particles with a "necklace" type configuration. It is predominantly the equilibrium beta-Mg2Si phase that precipitates during subsequent cooling at 1000 K h(-1) while orthogonal beta'-Mg2Si platelets are also noted starting at 500 K h(-1). The hardness decreases with decreasing cooling rate from 41.1 +/- 1 HV to 35.8 +/- 0.8 HV, by 15 pct, over the range investigated. The precipitation capacity retained in homogenized samples cooled to room temperature at less than 250 K h(-1) is reduced substantially. The solvus temperatures of these samples are below 773 K (500 degrees C) ensuring full solutionizing of the Mg2Si precipitates below the press exit temperatures typically employed by extruders. An 8-hour soaking at 853 K (580 degrees C) followed by cooling at 250 K h(-1) is identified to be the optimum homogenization treatment as it gives a homogeneous structure with predominantly spherical-shaped alpha(c)-Al-12(Fe,Mn)(3)Si particles and sufficiently low hardness for improved extrudability and a solvus temperature below 773 K (500 degrees C) to ensure adequate age-hardening capacity. DOI: 10.1007/s11661-012-1379-y (C) The Minerals, Metals & Materials Society and ASM International 2012