Performance of 6xxx Series Alloys Designed for Improved Extrudability and Strength
Malcolm J. Couper, Comalco Research & Technical Support,
Barbara Rinderer, Comalco Research & Technical Support,
John Heathcock, Comalco Aluminium Limited, and
Xinquan Zhang, Comalco Research & Technical Support
Track: BILLET PROCESS AND EQUIPMENT - Metallurgy
ABSTRACT --- In low-to-medium strength 6xxx series alloys, the mechanical
properties are determined by Mg-Si precipitates. Current alloy design is based on
“balanced” Mg and Si levels or an excess of Si in relation to Mg2Si (2:1 atomic ratio
of Mg to Si). It has been discovered that for a wide range of 6xxx series alloys, the
peak-aged condition is better described as containing Mg-Si precipitates with an
approximately 1:1 ratio of Mg to Si. A step-change improvement in properties and
extrudability has been achieved by designing alloys based on this new paradigm.
Industrial trials have confirmed the improvements, as reflected in 5% lower breakout
pressure and 10 to 20% increase in the maximum extrusion speed, without
compromising mechanical properties. Acceptance of the new alloys has been high
(currently 60,000 metric tons per annum) and international patent protection has
been granted in five countries to date.
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