Acta Physica Hungarica 71. (1992)
1-2. szám - Condensed Matter - Z. H. Ismail - B. Bouchra: Age-hardening characteristics of an AlMgSi alloy
Acta Physiea Hungarica 71 (1-2), pp. 3-7 (1992) AGE-HARDENING CHARACTERISTICS OF AN AlMgSi ALLOY Z. H. Ismail and B. Bouchra Department of Metallurgy, NRC, Atomic Energy Commission Cairo, Egypt (Received 20 June 1990) Age-hardening behaviour of an AlMgSi alloy was followed by hardness measurements during isochronal and isothermal ageing. The alloy is found to age-harden during natural ageing at room temperature after quenching from the solid solution temperature. The alloy exhibits peak hardness by artificial ageing at 200 °C for 2 hours. Isothermal ageing curves indicated that the rate of hardness increase at early stages of ageing, is dependent upon the ageing temperature in a manner which obeys an Arrhenius-type equation. An activation energy of 0.95 ± 0.05 eV was calculated from the Arrhenius plot of the results. This activation energy shows that the process responsible for hardness increase in the early stages of ageing may be controlled by the migration of solute-vacancy complexes. 1. Introduction The AlMgSi system is the basis for a major class of heat-treable alloys used for both wrought and cast products. These alloys are of great technological interest since they combine many favourable characteristics including moderately high strength, relatively low quench sensitivity and good corrosion resistance. In a previous work [1] the precipitation behaviour during ageing of the supersaturated solid solution of an AlMgSi alloy was investigated using transmission electron microscope. The aim of the present work was to follow the precipitation from solid solution during ageing at various temperatures, by hardness measurements. 2. Materials and experimental The material under investigation is cold-rolled sheets of AlMgSi alloy containing 0.98 wt % Si, 0.78 wt % Mg as major alloying elements and 0.31 wt % Mn and 0.06 wt % Fe as minor additions. Specimens of about 1 cm2 area were cut from the as-received sheet, and solid solution annealed at 570 °C for one hour in air muffle furnace whose temperature is controlled to ±5°C. The specimens were then quenched in water and were given 5 minutes standard delay at room temperature before artificial ageing. Artificial ageing was conducted in an air chamber furnace at temperatures from 100 up to 300 °C for various periods of time ranging from 5 minutes to 24 hours. The temperature of the furnace was controlled to ±5 °C. Acta Physiea Hungarica 71, 1992 Akadémiai Kiadó, Budapest