Papers by Author: X.K. Wu

Abstract: In the present case study, finite element (FE) simulation was performed to evaluate the design of a spreading pocket die by analysing the metal flow during the extrusion of the 6061 alloy to produce a thin-walled wide profile for ground transportation applications. The results obtained from the FE simulation were in good agreement with those from industrial extrusion trials. The velocity and temperature non-uniformities on the profile cross section, revealed from the FE simulation, suggested the die bearing area for die correction. The FE simulation also showed that ram speed had little influence on the velocity non-uniformity but a marked effect on the temperature and temperature distribution of the profile. In the case of extrusion through the spreading pocket die, more heat dissipation from the hotter billet to the die took place, especially when ram speed was low. Therefore, to reach a temperature sufficient for the dissolution of Mg and Si, ram speed must be raised. The FE simulation in the transient state of the extrusion process could give an indicative ram speed for trial extrusion to reach a sufficiently high temperature for the solution treatment on the one hand and to avoid hot shortness on the other hand. It also showed that ram speed had a moderate effect on the breakthrough pressure. Therefore, in the selection of ram speed, attention should be paid to its effect on the maximum profile temperature and temperature distribution.

Abstract: The effect of forward extrusion temperature and rate on the formability and microstructure of 7075 aluminum alloy was investigated by means of scanning electron microscopy (SEM), optical microscopy (OM) and hardometer. The results showed that the outflow rate was in the range of 6~2m/min with the extrusion temperature from 340°C to 420°C. Higher temperature resulted in lower critical extrusion force, decreased permissible extrusion rate and obvious drop in the formability. Lower temperature resulted in improvement in the formability but higher critical extrusion force, which might lead to shuttingdown of the extruder. There were no obvious effects of extrusion temperature and rate on the microstructure and hardness of the as-extruded alloy. It suggests that dynamic recovery or partial recrystallization occurred in the alloy during extrusion.