Papers by Author: Ji Yong Yao

Abstract: An aluminium alloy was sintered using a conventional press and sinter process, at various gas pressures, to observe the effect of sintering gas pressure on the densification rate. Compacts of aluminium alloy 2712 (Al-3.8Cu-1Mg-0.7Si-0.1Sn) were prepared from elemental powders and sintered in a horizontal tube furnace under nitrogen or argon at 590°C for up to 60 minutes, and air cooled. The gas flow was adjusted to achieve specific gas pressures in the furnace. It has been found that increasing the nitrogen pressure at the start of the isothermal holding stage to 160kPa increased the densification rate compared to standard atmospheric pressure sintering. Increasing the nitrogen pressure further, up to 600kPa, had no additional benefit. The densification rate was increased significantly by increasing the gas pressure to 600kPa during both heating and isothermal holding. Under argon the elevated pressure did not increase the densification rate. Results seem to suggest that the beneficial effect of the elevated pressure on the rate of densification is related to nitride formation.

Abstract: Alloys designed to optimise strength and extrudability have a lower alloy Mg to Si ratio than has commonly been used in AA6060 and AA6063 alloys. Intermetallic phases have an impact on alloy design since they tie up some of the Mg and Si alloy content. The effect of Mg and Si alloy content on the type of intermetallic phases present has been investigated using TEM, SEM and Thermocalc analysis. Results for Al-Mg-Si-Fe alloys with 0.46 - 0.70 wt%Mg, 0.27 - 1.24 wt%Si and 0.09 - 0.22 wt%Fe are presented. The occurrence of a-AlFeSi (various stoichiometries), b- Al5FeSi, p-Al8FeSi6Mg3, Mg2Si and Si has been found to depend on alloy composition within the ranges examined.