Elsevier

Materials Science and Engineering: A

Volume 559, 1 January 2013, Pages 902-908
Materials Science and Engineering: A

Industrial processing of a novel Al–Cu–Mg powder metallurgy alloy

https://doi.org/10.1016/j.msea.2012.09.049Get rights and content

Abstract

The objective of this work was to develop an aluminum powder metallurgy (P/M) alloy appropriate for industrial press-sinter technology. An entry in the 2xxx series of aluminum–copper–magnesium alloys was explored for this purpose. Designated as P/M 2324 (Al–4.4Cu–1.5Mg), the sintering response and mechanical properties of the alloy were investigated in laboratory and industrial settings. It was determined that compaction at 400 MPa and sintering at 600 °C for 20 min produced the best properties in the sintered product. Doping with a minor amount of tin (0.2w/o) was found to improve the properties whereas modifications to Cu and Mg concentration produced minimal gains. All tensile properties of P/M 2324 were significantly superior to those of the principal 2xxx series aluminum P/M alloy (AC2014) in current use. These benefits were attributed to a high sintered density (>98% theoretical) that was reproducible in an industrial setting.

Introduction

Aluminum powder metallurgy (P/M) is a metal forming technology that is principally employed in the manufacture of high volume automotive parts wherein a balance between tight dimensional tolerances and excellent mechanical properties is sought. Its application has risen steadily since the 1990s when it was first utilized in two OEM programs [1], [2]. Aluminum P/M is now regarded as a reliable, robust, and cost effective technology that is employed in many different engine platforms. Despite such success, it remains heavily focused on the production of a singular component—camshaft bearing caps. This limitation has generally been attributed to the limited number of aluminum P/M alloys that have been commercially available and the correspondingly narrow scope of mechanical properties that these systems encompass. In fact, commercial P/M production has mainly relied on the use of a singular alloy known as AC2014 (Al–4.4Cu–0.8Si–0.6Mg). Modeled after the wrought alloy AA2014, this blend is available from several commercial suppliers, is known to exhibit a strong response to P/M processing, and offers reasonable mechanical properties after sintering [3].

To broaden the range of applications for aluminum P/M technology considerable research efforts have emphasized the development of new aluminum P/M alloys that offer improved mechanical performance. In one key area the development of novel alloys within the Al–Zn–Mg–Cu system has been targeted [4], [5], [6]. Here, researchers have attempted to leverage the same metallurgical principals (i.e. GPB/η-type precipitates) that invoke the high strength observed in wrought counterparts from the 7xxx series. Other studies have investigated the development of alloys from the Al–Si–Mg–Cu family [7], [8], [9], [10]. The main driving force in this instance is the desire to devise P/M alloys that can compete directly with die cast Al–Si-based materials. Several of these programs have recently matured into commercial products wherein the base P/M alloy chemistries bear resemblance to wrought AA7075 and die cast A390. Relative to AC2014, these new materials offer appreciable mechanical gains yet certain limitations remain. These include a higher purchase price and P/M processing constraints such as reduced green strength and compressibility [6] as well as the need for extended sintering periods [7].

Surprisingly, there has been somewhat less of an effort dedicated to the development of alloys from the system upon which the last two decades of industrial growth for aluminum P/M technology has been built; namely, the Al–Cu–Mg family of alloys. Therefore, the objective of this study was to develop a new Al–Cu–Mg aluminum P/M alloy with core attributes that targeted a simplistic alloy chemistry, a strong response to P/M processing, and tangible mechanical gains over AC2014. As a starting point, the experimental P/M system was modeled after the wrought alloy AA2324 given that this alloy is one of the strongest members of the 2xxx series of wrought aluminum alloys [11].

Section snippets

Materials

The P/M alloy studied in this work was denoted as P/M 2324 and had a nominal bulk composition of Al–4.4Cu–1.5Mg in most instances. To produce the base blend, three powders were used. These were elemental aluminum and magnesium as well as an aluminum–copper master alloy. In some experiments minor additions of tin were assessed. Elemental tin powder was utilized for this purpose. All elemental powders were of a minimum reported purity of 99.5%. The wax used for tooling lubrication purposes was

Experimental techniques

In this work, standard “press and sinter” processing practices were employed. Initially, raw powders were weighed to the desired alloy chemistry, placed into a Nalgene® bottle, and blended in a Turbula® mixer-shaker for 30 min. The blends were then uni-axially compacted in self-contained tooling using an Instron® 5594-200 HVL, 1MN load frame. Specimen geometries consisted of 31.7 mm×12.7 mm×10 mm transverse rupture strength (TRS) bars and flat dog bone bars produced according to MPIF standard 10.

Laboratory sintering trials

Previous work has shown that all compaction attributes (powder flow, apparent density, green strength, etc.) of P/M 2324 were reasonable and comparable to industrial variants of the commercial P/M alloy AC2014 [12]. As such, initial studies in this work focused on the general sintering response of the new alloy emphasizing the effects of sintering time and temperature. A compaction pressure of 400 MPa was chosen to complete these preliminary studies as it corresponded to the practical upper

Conclusions

Through the work completed in this study the following conclusions have been reached:

  • (1)

    The most appropriate laboratory-based processing route for P/M 2324 included a compaction pressure 400 MPa (Fig. 10) followed by sintering at 600 °C (Fig. 2) for 20 min (Fig. 6).

  • (2)

    Under similar parameters, P/M 2324 also exhibited an excellent sintering response in an industrial setting (Table 2).

  • (3)

    Modification of the bulk Cu and Mg concentrations produced little improvement over the standard P/M 2324 chemistry (Table 3

Acknowledgments

The Natural Sciences and Engineering Research Council of Canada (NSERC) are acknowledged for the provision of funding support through Discovery Grant # 250034. The authors would like also to acknowledge technical support at Dalhousie University from Mrs. Patricia Scallion and Mr. Dean Grijm.

References (18)

  • A.D.P. LaDelpha et al.

    Eng. Appl. Sci. A

    (2009)
  • D.W. Heard et al.

    J. Mater. Process.

    (2009)
  • T.B. Sercombe et al.

    Mater. Sci. Eng. A

    (1999)
  • I.A. MacAskill et al.

    J. Mater. Process. Technol.

    (2010)
  • T.B. Gurganus

    Adv. Mater. Process.

    (1995)
  • C. Lall et al.

    Int. J. Powder Metall.

    (2000)
  • D.P. Bishop, B. Hofmann, K.R. Couchman, Properties and attributes of commercially available AC2014-type aluminum P/M...
  • G.B. Schaffer et al.

    Powder Metall.

    (1999)
  • J.M. Martin et al.

    Powder Metall.

    (2002)
There are more references available in the full text version of this article.

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