Abstract
It is well known that the hot workability of an aluminum alloy strongly depends on its Mg content. In this paper, the changes of extrudability and mechanical properties of extrusions of commercial Al-Zn-Mg alloys with the increase of Mg content were investigated in a wide range of 0.41-2.00%Mg. Extrusion experiments were carried out by using a 1600 ton press. Extrudability was evaluated by the maximum extruding pressure and maximum extruding rate. The obtained results are summarized as follows.
(1) With the increase of Mg content, the extrudability of Al-Zn-Mg alloys declined, particularly a remarkable decrease in the maximum extruding rate which is directly related to the industrial productivity was observed. The maximum extruding rate increased in a low Mg range of 0.4-1.2% and still more at lower extruding temperature near 410°C. An approximate linear relationship was empirically obtained between the maximum extruding pressure and the logarithm of Mg content.
(2) Tensile strength and 0.2% proof stress of the extrusions were generally higher for higher Mg content. But for a higher Mg content between 1.2 and 2.0%, these stresses strongly depended on the extrusion temperature and rate, and in case of low extruding temperature and rate, strength decreased due to insufficient quenching and incomplete dissolution of precipitates during extrusion.
(3)Alloys containing 0.7-1.0%Mg showed both excellent extrudability and high strength; the maximum extruding rate higher than 20m/min and 0.2% proof stress higher than 25kg/mm2. For these alloys, suitable extrusion temperature is between 410 and 450°C.
