The aim of this thesis was to improve the properties of pressed and sintered aluminium powder alloys. This improvement was to be achieved using two methods. The first method involved the selection of an alloy system using binary aluminium phase diagrams and a knowledge of the phase diagram characteristics of ideal sintering systems. The second approach involved the judicious use of selected trace element additions to modify the sintering characteristics of aluminium and its alloys. A trace amount of magnesium was found to be critical to the sintering of aluminium powder due to its disrupting effect on the tenacious oxide layer covering the powder particles. The critical amount of Mg required to optimise both density and mechanical properties is dependent on the specific volume of oxide and the therefore particle size. The optimum concentration is 0.1-1.0wt% Mg. The Al-Sn phase diagram exhibits many of the characteristics of an ideal sintering system. Unsurprisingly, Sn was found to be an extremely efficient sintering aid, but only in the presence of Mg. Near full density parts were produced using an Al-8Sn-0.15Mg alloy in short sintering times (30 minutes). Additionally, as-sintered ductilities exceeding 20% were achieved using an Al-2Sn-0.15Mg alloy. Alloys based on the Al-Sn-Mg system lend themselves to sintering without compaction and therefore freeformed Al-Sn-Mg alloys have been produced and sintered to near full density from a starting density of ~50%. Trace amounts of Sn (Pb, In, Bi, or Sb) enhance the sintering response of an Al-4Cu-0.15Mg alloy via a vacancy binding mechanism. A similar mechanism suppresses natural ageing and stimulates artificial ageing when trace amounts of Sn are added to this alloy. A Sn-modified 2XXX series alloy has also been produced with mechanical properties nearly 20% above current commercial alloys. Along with the addition of 0.1wt%Sn, this improvement required an alteration to the solution treatment cycle which allowed the use of a higher sintering temperature without the formation of large amounts of boundary phase.

Extrusion is a continuous solid state deformation process which is widely used in the aluminium industry. The demand for aluminium extrudates are growing and extruders are pressurized to extrude products as fast as possible without lowering the quality of the product. Important extrusion parameters and conditions are exit temperature, extrusion speed and alloy composition. It is widely accepted in extrusion industry that extrusion surface defects increase when the extrusion speed and exit temperature are increased for a constant alloy. One of the major surface defects is the so-called die pick-up and it is presently uncertain if increase with extrusion speed (from a low 25m/min) would result in an increase of the number of die pick-up defect.Die pick-up appears like a scratch mark or comet on the surface of the extrudate which damages the appearance. Previous research suggests that second phase particles, eutectic reactions (555°C - 600°C), extrusion process conditions and die conditions may influence the cause of die pick-up. However the influencing factors for die pick-up are not well established.The research started by determining the lowest melting temperature for AA6060 alloy as this temperature limit the highest temperature above which incipient melting starts. This temperature corresponds to the eutectic melting temperature for AA6060 alloy. Eutectic melting was only detected above 610°C and therefore the exit temperature could be increased to a maximum of 610°C. For an AA6xxx alloy system the lowest melting temperature is 555°C if Mg2Si and excess silicon were present. However as Mg2Si may have fully dissolved into the solid solution, no reaction can take place.A preliminary investigation was conducted to study the characteristics of the newly installed extrusion control and monitoring system. Through this study the relationship between the set extrusion speed and the actual extrusion speed was established. It was found that the actual extrusion speed was lower than the set extrusion speed and was further complicated by the capacity limit of the extrusion pressure. Exit temperature measurements were accurate, however it was measured about 1m away from the die exit. Experiments were carried out to estimate the exit temperature drop and hence the exit temperature measurements were corrected accordingly.Thus, the aim of the present research was to establish the relationship between die pick-up and extrusion conditions (extrusion speed, exit temperature and die condition) and to propose the likely formation mechanism for die pick-up.In this research AA6060 alloy was used and was extruded at 25m/min, 30m/min, 35m/min, 40m/min and 45m/min. The exit temperature was found to increases from 542°C to 567°C. Three types of die pick-up was identified which were named as normal pick-up, die line pick-up and lump pick-up. Normal pick-up occurred regardless of the extrusion speed and exit temperature; however the amount of normal pick-up did not increase when the extrusion speed was increased. Die line pick-up occurred when the extrusion speed was 45m/min and appeared only on the die lines. Lump pick-up is not significant since it was very rare.AA6060 (0.4%Mg and 0.5%Si) alloy has about 0.27% excess silicon and therefore at 555°C, Mg2Si particles react with aluminium and excess silicon to form liquid. However normal pick-up and die line pick-up still occurred at temperatures lower and higher than 555°C and therefore it confirms that eutectic reactions do not influence formation of pick-up. Therefore die pick-up is most likely to be caused due to a mechanical process rather than a metallurgical process.

The aim of this thesis was to improve the properties of pressed and sintered aluminium powder alloys. This improvement was to be achieved using two methods. The first method involved the selection of an alloy system using binary aluminium phase diagrams and a knowledge of the phase diagram characteristics of ideal sintering systems. The second approach involved the judicious use of selected trace element additions to modify the sintering characteristics of aluminium and its alloys. A trace amount of magnesium was found to be critical to the sintering of aluminium powder due to its disrupting effect on the tenacious oxide layer covering the powder particles. The critical amount of Mg required to optimise both density and mechanical properties is dependent on the specific volume of oxide and the therefore particle size. The optimum concentration is 0.1-1.0wt% Mg. The Al-Sn phase diagram exhibits many of the characteristics of an ideal sintering system. Unsurprisingly, Sn was found to be an extremely efficient sintering aid, but only in the presence of Mg. Near full density parts were produced using an Al-8Sn-0.15Mg alloy in short sintering times (30 minutes). Additionally, as-sintered ductilities exceeding 20% were achieved using an Al-2Sn-0.15Mg alloy. Alloys based on the Al-Sn-Mg system lend themselves to sintering without compaction and therefore freeformed Al-Sn-Mg alloys have been produced and sintered to near full density from a starting density of ~50%. Trace amounts of Sn (Pb, In, Bi, or Sb) enhance the sintering response of an Al-4Cu-0.15Mg alloy via a vacancy binding mechanism. A similar mechanism suppresses natural ageing and stimulates artificial ageing when trace amounts of Sn are added to this alloy. A Sn-modified 2XXX series alloy has also been produced with mechanical properties nearly 20% above current commercial alloys. Along with the addition of 0.1wt%Sn, this improvement required an alteration to the solution treatment cycle which allowed the use of a higher sintering temperature without the formation of large amounts of boundary phase.

Techn. Universiẗat, Diss., 2006--Darmstadt.

Zugl.: Dresden, Techn. Univ., Diss., 2008

Thèse (M.A.)--Université Laval, 2007. / Bibliogr.: f. 103-107. Publié aussi en version électronique dans la Collection Mémoires et thèses électroniques.

Universiẗat, Diss.--Hannover, 1996.

Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2007. / La p. de t. porte en outre: Mémoire présenté à l'Université du Québec à Chicoutimi comme exigence partielle de la maîtrise en ingénierie. CaQQUQ Bibliogr.: f. 101-106. Document électronique également accessible en format PDF. CaQQUQ

Mémoire (M.Sc.A.)-- Université du Québec à Chicoutimi, 1988. / Document électronique également accessible en format PDF. CaQCU

Mémoire (M.Eng.) -- Université du Québec à Chicoutimi, 1992. / Résumé disponible sur Internet. CaQCU Document électronique également accessible en format PDF. CaQCU