Aluminum (Al) powder metallurgy (PM) provides a cost effective and environmentally
friendly means of creating lightweight, high performance, near net shape components,
relative to conventional casting/die casting technology. Unfortunately, the current lack of
commercially available Al alloy powder blends has hindered development in this field as
a result of the limited scope of mechanical properties available; especially under elevated
temperature conditions common to many automotive applications. As such, the objective
of this research was to attempt to improve the versatility of current Al PM technology
through the incorporation of Fe and Ni transition metal additions into an emerging Al-
4.4Cu-1.5Mg-0.2Sn alloy, as this technique is known to enhance the elevated temperature
stability of wrought/cast Al alloys through the formation of stable, Fe/Ni aluminide
dispersoids.
Initial experimentation consisted of evaluating the feasibility of incorporating Fe and Ni
both elementally and pre-alloyed, through a series of tests related to their PM processing
behaviour (compressibility, sintering response) and sintered product performance
(ambient tensile properties). Results confirmed that pre-alloying of the base Al powder
was the most effective means of incorporating Fe and Ni as all such specimens achieved
properties similar or slightly superior to the unmodified alloy. Of the pre-alloyed systems
considered, that containing 1%Fe+1%Ni displayed the most desirable results in terms of
mechanical performance and microstructural homogeneity of the Fe/Ni dispersoid phases
present in the sintered product.
Bars of the baseline system and that modified with pre-alloyed additions of 1Fe/1Ni were
then sintered industrially to gain a preliminary sense of commercial viability and obtain
additional specimens for elevated temperature exposure tests. Results confirmed that the
sintering response, tensile properties and microstructures were essentially identical in
both alloys whether they were sintered in a controlled laboratory setting or an industrial
production environment. Furthermore, DSC data indicated that S (Al2CuMg)-type phases
were the dominant precipitates formed during heat treatment. The effects of elevated
temperature exposure were assessed in the final stage of research. Both alloys were
found to exhibit comparable behaviour when exposed to the lowest (120°C) and highest
(280°C) temperatures considered. Here, the alloys showed no obvious degradation at
120°C. Conversely, exposure at 280°C prompted a steady decline in yield strength for
both alloys with significant precipitate coarsening noted as well. Despite these
similarities, differences emerged during isochronal tests at intermediate temperatures.
Here, DSC data indicated that the precipitates present in the pre-alloyed material were
stable at temperatures up to 160°C while those in the unmodified alloy had begun to
overage under the same exposure conditions. These differences were accompanied by
increased stability in tensile yield strength for the pre-alloyed material. In all, this study
has indicated that the use of Al powder pre-alloyed with Fe/Ni additions is feasible for
press-and-sinter PM technology and that the sintered product exhibits improved elevated
temperature stability under certain conditions.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:NSHD.ca#10222/15049 |
| Date | 21 June 2012 |
| Creators | Moreau, Eric D. |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_US |
| Detected Language | English |
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