Research Papers: Friction & Wear

Effect of Precipitates on Mechanical and Tribological Performance of AZ91 Magnesium Alloy–Steel Couple

[+] Author and Article Information
Deepak Kumar, Tulsi Bisht

Industrial Tribology,
Machine Dynamics and Maintenance
Engineering Centre,
Indian Institute of Technology Delhi,
New Delhi 110016, India

Jayant Jain, Anuz Zindal

Department of Applied Mechanics,
Indian Institute of Technology Delhi,
New Delhi 110016, India

1Coresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received August 6, 2014; final manuscript received November 23, 2014; published online January 27, 2015. Assoc. Editor: Satish V. Kailas.

J. Tribol 137(2), 021604 (Apr 01, 2015) (7 pages) Paper No: TRIB-14-1197; doi: 10.1115/1.4029248 History: Received August 06, 2014; Revised November 23, 2014; Online January 27, 2015

The present work involves the study of the effect of precipitates on mechanical and tribological properties of AZ91 magnesium alloy. Optical microscopy, scanning electron microscopy (SEM), and nanoindentation were used to characterize the microstructures and mechanical properties of the alloy. In addition, the wear behavior of the alloy was deduced using a pin-on disk tribological configuration under unidirectional sliding against steel (AISI 250). The elastic modulus of AZ91 alloy was found to vary significantly with changing precipitation state. The tribological evaluations showed that the specific wear-rate of solutionized sample is lowest as compared to the aged samples. This was attributed to the absence of γ-Mg17Al12 phase. Examination of worn surfaces suggested that microploughing coupled with the adhesive mode of wear is the main wear mechanism in the aged samples.

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Fig. 1

Optical micrographs of AZ91 magnesium alloy: (a) as-cast and (b) solution treated at 420 °C for 24 h

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Fig. 2

Analysis of as-cast AZ91 alloy: (a) SEM micrograph, (b) area mapping in EDS, (c) and (d) elemental mapping of circled regions in EDS

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Fig. 3

EDS analysis of solution treated AZ91 alloy: (a) SEM micrograph, (b) area mapping in EDS, (c) and (d) elemental mapping of circled regions in EDS

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Fig. 4

Aging curve of AZ91 alloy at 250 °C. Note that the curve through data points is to guide the eye. The AQ represents as-quenched condition.

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Fig. 5

SEM micrographs of samples aged at 250 °C for (a) 12 h, (b) 48 h, and (c) 72 h. The arrows indicate the presence of continuous and discontinuous precipitates.

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Fig. 6

(a) Nanoindentation load-depth curve for samples aged at 250 °C for 0 h (as quenched), 12 h, 48 h, and 72 h and (b) the hardness and elastic modulus values obtained from indentation data in (a) plotted with aging time.

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Fig. 7

Specific wear-rate and coefficient of friction plotted against aging time. Note that AR and AQ represent as-received and as-quenched samples, respectively.

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Fig. 8

A free body diagram illustrating the various forces existing on a sliding interface

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Fig. 9

SEM micrographs of worn surfaces after 6 h of wear test on: (a) as-received, (b) solution treated, (c) 12 h aged, (d) 48 h aged, and (e) 72 h aged samples



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