EFFECT OF REDUCTION RATIO AND DIE ANGLE ON THE PROPERTIES OF EXTRUDED Al-Mg-Zn ALLOY

Abstract

Hardness, microstructure and corrosion response of extruded Al-Mg-Zn alloy at varied die angle and reduction ratio has been investigated. Medium carbon steel dies (𝜎𝑐= 450Mpa, 𝜎𝑦=176Mpa) with entry angles of 600, 750, 900, 1050, 1200, 1500, 1800 and reduction ratios of 0.21, 0.40, 0.48 and 0.62 were used. Extrusion on the alloy was done hot and the extruded samples from the various die angles and reduction ratios were subjected to hardness test, electrochemical test for corrosion and microstructural analysis. Results show that increasing the die angle reduced the extrusion pressure to a minimum value of 900, beyond which the pressure increased with further increase in the die angle, and extrudate hardness increases with increasing die angle and reduction ratio. Considering the electrochemical test, the corrosion potential shifted in the positive direction with increase in the die angle and reduction ratio indicating that anodic process is more affected than the cathodic process while the Tafel slopes remained unchanged. There was improvement in the corrosion resistance of the extruded alloy compared to the as-cast condition but the corrosion rates under extruded condition does not follow a particular pattern as it was lower with 900 die angle and higher with 1500 die angle, however the corrosion rate increased with increase in the reduction ratio