Prediction of wear coefficient of Al6061–TiO₂ composites

Abstract

In recent years, aluminum alloy based metal matrix composites (MMC) are gaining wide spread acceptance in several interesting applications such as piston, connecting rod, microwave filters, vibrator component, contactors, impellers and space structures. These composites possess excellent wear resistance in addition to other superior mechanical properties such as strength, modulus and hardness when compared with conventional alloys. Of all the aluminum alloys, 6061 is quite popular choice as a matrix material to prepare MMCs owing to its better formability characteristics and option of modification of the strength of composites by adopting optimal heat treatment. From the literature, it is quite evident that the focus has been centered on processing of MMCs and characterization of mechanical properties of MMCs.

Tribological characteristics of several MMC systems involving glass, flyash, SiC, Al₂O₃ as discontinuous dispersoids have been reported. However, meagre data are available as regards the theoretical prediction of wear rate of MMCs. Prediction of wear rate gains impetus in present industrial scenario to assess the life of sliding components in advance to avoid huge economic losses that incur due to wear.

In the light of the above, the present investigation deals with preparation of Al6061–TiO₂ composites by liquid metallurgy route. The extent of incorporation of TiO₂ in the composite was varied from 2 to 10 wt%. Microstructure studies, hardness and wear test were conducted on the cast Al6061–TiO₂ composites. Pin on disc machine was used to assess the wear resistance of the prepared composites. Load was varied from 10 to 40 N while the sliding distance was from 90 to 540 m. Wear coefficients were evaluated by using Archard's and Yang's theoretical models. Increased contents of TiO₂ resulted in higher hardness and lower wear coefficient of the composites under identical test conditions. The wear coefficient of all the Al6061–TiO₂ composites studied decreased at higher loads and larger sliding distances. The predicted values of the wear coefficient are in close agreement with the experimental ones.

Introduction

Aluminium alloys have excellent mechanical properties coupled with good corrosion resistance. However, they possess poor wear and seizure resistance. To improve the above said properties, researchers have successfully dispersed various hard and soft reinforcements such as SiC, Al₂O₃, flyash, glass, WC, graphite, mica, coconut shell char in aluminium alloys by different processing routes [1], [2], [3]. Of all the processing routes, liquid metallurgy method is the most sought after owing to its several advantages such as economical, mass production, near net shaped components can be produced [4]. Use of TiO₂ as reinforcement in aluminium alloys has received little attention although it possess high hardness and modulus with superior corrosion resistance [3]. Of all the aluminum alloys, 6061 is quite popular choice as a matrix material to prepare metal matrix composites owing to its better formability characteristics and option of modification of the strength of composites by adopting optimal heat treatment [5].

In recent years, aluminum alloy based metal matrix composites (MMCs) are being explored as candidate materials in several interesting applications such as piston, connecting rod, contactors, where sliding is a key component [3]. Excessive wear due to sliding will ultimately result in seizure of the mating parts sometimes leading to catastrophic failure [6]. Hence, prediction of the wear behaviour of the sliding components is of utmost importance avoiding huge economic losses. Tribological characteristics of several MMC systems involving glass, flyash, SiC, graphite, mica, Al₂O₃ as discontinuous dispersoids have been reported [7], [8], [9], [10]. However, meagre data is available as regards the theoretical prediction of wear behaviour of MMCs. Recently, Yang has developed a theoretical model predicting the wear behaviour of MMCs based on the modification of Archard's wear model [11]. It is reported that wear coefficient is a better measure of wear behaviour of materials as it takes care of both the material properties and the operating conditions [11]. Based on the above considerations, this study was conducted to investigate the effects of weight fractions of TiO₂, load and sliding distance on the experimental and predicted wear coefficient of the developed cast Al6061–TiO₂ composites.