T. K. Dan

Aluminium alloy-solid lubricant talc particle composites

This paper describes the method of synthesizing cast aluminium alloy talc particulate composites and their mechanical and wear properties. Talc particles were characterized using X-ray diffraction, infrared spectroscopy and differential thermal analysis techniques. Composites with two Al-Si alloys (LM 13 and LM 6) as matrices were prepared by heating the molten alloys to 750° C and adding the preheated talc powder (−150 + 50 μm size) after creating a vortex by mechanically stirring the melt. Simultaneous addition of 2 wt% Mg was found to facilitate the introduction and dispersion of talc particles in molten Al-Si alloys. Composites containing 2.8 wt % talc in LM 13 and 2 wt % talc in LM 6 have been prepared. Optical micrographs of composites revealed uniform distribution of talc particles. Hardness and tensile strength of LM 13+2.8% talc were 85 BHN and 126 MPa, respectively. After suitable heat treatment hardness and strength were increased to 125 BHN and 211 MPa respectively. Wear rates of LM 13+2.8 wt% talc and LM 6+2 wt % talc composites were found to be 22 to 30% less than the wear rates of corresponding base alloys without any dispersions.

Influence of solutionizing temperature and duration on the microstructure and properties of a hypereutectic aluminium-silicon alloy-graphite composite

Graphitic Al-Si alloys are well known for their good antifriction and sliding wear characteristics [1-4]. They have been found to be potential engineering materials for automotive applications such as cylinder liners [1], bushings and bearings [5] and pistons [6]. The selection of a heat-treatable variety of A1-Si alloy matrix for the synthesis of graphitic A1 alloys is always desirable, since deterioration in properties of the composites due to the addition of graphite can be compensated for at least partially be means of suitable heat treatments. T6 heat treatment (solutionizing followed by artificial ageing) is very widely adopted for the purpose as regards the AI-Si alloy composites. It may be noted that the optimization of the solutionizing temperature is essential and critical. This is because a lower solution treatment temperature leads to incomplete dissolution of metastable phases and a reduced degree of homogenization of the matrix, whereas a higher temperature causes partial melting [7, 8]. Interestingly, the ill-effects of higher solutionizing temperatures cannot be remedied by any means, and the casting has ultimately to be rejected. Thus, although problems related to the proper selection of solutionizing temperatures are so crucial, practically no information appears to be available on the subject as regards graphitic A1 alloys. In view of the above facts, an attempt has been made to examine the influence of solutionizing parameters such as the temperature and duration of soaking on the microstructure and properties of a BS LM30 (A1-17.0 Si-4.5 Cu-0.5 Mg-0.1 Ni-0.3 Fe-0.1 Mn) alloy dispersed with 3.0 wt % graphite particles (size 45-150tzm). The composite was prepared by the liquid metallurgy route in the form of cylindrical bars (20 mm in diameter and 150 mm long). The solutionizing temperatures selected were 490,510 and 530 °C, and the soaking time was varied from 1 to 16 h. The dendritic structure of the as-cast composite containing needle-shaped eutectic Si particles and platelets and cuboids of primary Si phase in the matrix may be seen in Fig. 1. The figure also reveals the tendency of the primary Si particles to segregate close to graphite particles and, in some cases, closely entangle with the latter. This could be attributed to easy nucleation centres provided by the graphite particles to the first solidifying primary Si. Solutionizing the composite at 530 °C beyond 4 h

Aluminium alloy-silica sand composites: preparation and properties.

Ceramic particulate composites containing up to 25 wt% silica sand in commercially pure aluminium (LM-O) and its eutectic silicon alloy (LM-6) were prepared by liquid metallurgy techniques. Pre-treated sand particles of sizes ranging from −180 to +90μm were added to the alloy melts, followed by pouring the resulting mix into permanent moulds. Quantitative metallographic examination revealed that sand particles were uniformly distributed in both types of cast composite. Scanning electron microscopic examination of the composites showed voids around the sand particles. Tensile specimens, when fractured in an Instron machine, showed an interfacial mode of failure of the composite without affecting the sand particles, indicating poor bonding with the matrices. The hardness of LM-O alloyed with magnesium increased from 52 to 78 BHN, whereas the ultimate tensile stress (UTS) decreased from 92 to 62 MPa as a result of the addition of 20 wt% sand particles. In the case of LM-6-sand composites, the hardness remained almost constant but the UTS decreased from 184 to 112 MPa with the addition of 20 wt% sand particles. The compressive strength of both types of composite also decreased as a result of sand additions. However, a favourable effect of magnesium alloying on the strength of the cast composite was also observed.

Corrosion characteristics of aluminium alloy graphite particulate composite in various environments

The present study was aimed at understanding the response of 2014 Al alloy dispersed with graphite particles in various corrosive environments. Marine (sodium chloride) as well as acidic media were selected for the purpose with a view to widen the range of utility of the composite for applications where such environments may be encountered. Studies were also extended to characterize the corrosion resistance of the composite in fresh as well as used lubricating oils to explore the possibilities of using it in bearing, bushing and such other applications. The corrosion behaviour of the base alloy processed under identical conditions was also examined in the above media to see the influence of graphite addition in the alloy. In order to assess the role of the matrix microstructure, the composite as well as the base alloy was subjected to corrosion in heat-treated as well as-cast conditions. It was observed that the specimens suffered from the maximum rate of corrosion in acid, while sodium chloride produced the minimum corrosion rate. Oil in both used and fresh conditions revealed a negligibly small extent of corrosion. The composite was found to show a higher rate of corrosion than the base alloy under identical test conditions. This was attributed to the dispersoid/matrix interfacial corrosion in the case of the graphitic aluminium alloy. Heat treatment of the composite and the base alloy was found to lower the rate of corrosion in the environments tested. Microstructural modifications of the matrix and possible relief of residual stresses were thought to be responsible for the lower rate of corrosion in the heat-treated condition.

Effect of glass, rice-husk ash and wollastonite on transverse strength of porcelain

In o rde r to reduce energy consumpt ion , a t t empts are now being made at add ing at t i t ives to ceramics. In the previous studies we have observed tha t add i t i on o f a small percentage o f addi t ivies such as glass, r ice-husk ash and wol las toni te to porce la in can reduce the firing t empera tu re of the t r iaxial body to a grea t extent [1, 2]. In this let ter the effect o f add i t ion o f glass, r ice-husk ash and wol las toni te on the s t rength and bond ing o f porce la in has been observed. A t t e m p t s have been made to app ly the Spr igg s equa t ion for the s t rength o f such compos i tes and s t r e n g t h d e n s i t y dependence is observed. The fracture surfaces o f these composi t ies have been observed by scanning e lec t ron microscopy . China clay, flint, ball clay, waste glass powder and wol las toni te were ob t a ined f rom different sources and their chemical analysis was pe r fo rmed using the wet chemical analysis m e t h o d (Table I). Rice husk ash was p repa red by firing washed rice husk. R a w mate r ia l s were separa te ly g r o u n d to pass t h rough a 200 mesh B.S. Sieve. The conven t iona l porce la in mix (china clay 50%, fe ldspar 25% and flint 25%) was taken as the base mater ia l . Different po r t ions o f r ice-husk ash, glass and wol las ton i te were a d d e d to the porce la in (Table II) . The specimens were p repa red in the form o f rods by slip cast ing, using p las ter o f par is moulds . To ob t a in the p rope r consis tency o f the slip, a small quan t i t y o f e lectrolyte (1 :1 ra t io sod ium ca rbona t e and sod ium silicate mixture) was found essential in each case, bu t the a m o u n t var ied with the compos i t i on o f the body . The specimens were dr ied at 110 ° C for 48 h and were fixed at different t empera tu res between 1000 and 1200 ° C in