EFFECT OF TEMPERATURE ON SYNTHESIS AND PROPERTIES OF ALUMINUM-MAGNESIUM MECHANICAL ALLOYS

Swati Umbrajkar

New Jersey Institute of Technology, Newark, NJ

Advisor: Dr. Edward L. Dreizin

Abstract

The temperature histories of the milling jars used for synthesis of Al-Mg mechanical alloys are determined.  The effects of the temperature on the alloying progress and on the properties of the produced materials are considered.  Wireless temperature sensors are attached to the milling jars of a planetary mill to continuously monitor the milling temperature.  Different regimes of cooling of the milling jars are used including added custom-designed finned heat sinks and an external air conditioner.  Final and intermediate products were collected and analyzed using electron microscopy and x-ray diffraction.  The temperature history of the milling jar exhibits two peaks during mechanical alloying in the Al₇₀Mg₃₀ system.  The first peak is produced when the starting powders are flattened and flakes are produced.  The second peak is observed when the flakes are broken apart and the fragments are consolidated into the layered composites that serve as precursors for the mechanically alloyed particles.  The temperature of milling was found to strongly affect the magnesium solubility in the produced Al-Mg mechanical alloys.  The decrease of the milling temperature by 50 ºC resulted in the five-time increase in the achieved solubility with the observed maximum close to 25 atomic % for the Al₇₀Mg₃₀ composition.  The formation of intermetallic phases is favored at higher milling temperatures, when the high solubilities cannot be achieved.