Sunil Mohan

The effect of lead content on the wear characteristics of a stir-cast Al-Pb alloy

Abstract The present investigation was carried out to determine the effect of lead content in stireast Al-Pb alloys. It was found that dispersion of about 8–20 wt.% Pb in commercial aluminum modifies the wear characteristics of aluminum by introducing a transition from mild to severe wear with increasing sliding velocity. Beyond 20 wt.% Pb, the bulk wear was found to increase gradually.

Tribological behaviour of conventional Al-Sn and equivalent Al-Pb alloys under lubrication

Two compositions of conventional aluminium base alloys were selected and equal amounts of tin and lead as a soft phase were incorporated separately. Impeller mixing and chill casting technique were employed for the preparation of the alloys. Mechanical properties of as cast alloys were evaluated at room temperature. Frictional behaviour of the alloys was studied in detail under lubrication while creating different frictional states by imposing 5–60 kg of normal load on the bearing (bush) mating surface. It was found that aluminium tin and leaded aluminium alloys slightly differ in mechanical properties. Frictional states created during sliding against steel shaft (hardness 55–60 Rc) under oil lubrication were not much different. Leaded aluminium alloy bushes show marginally lower friction than the conventional ones.

Wear characteristics of HSLA steel

HSLA steel being a promising material in numerous applications, was subjected to wear studies under dry sliding conditions at varying conditions of loads and sliding speeds. Wear debris were extensively studied under optical, stereo- and scanning electron microscopes and also by X-ray diffraction. In order to understand the wear mechanism, wear tracks were examined under optical and scanning electron microscopes. In addition, depth of strain hardened zone below sliding surface was measured under different conditions of loads. This study showed that wear rate initially increased either with increased load or sliding speed and debris generated was a mixture of oxide and metal powders, but after attaining a peak in wear rate, a decreasing trend was observed for load as well as sliding speed studied. This decreasing trend has been attained due to domination of oxidation process as a result of rise in temperature at higher values of loads and sliding speeds. These oxides formed with temperature rise covered the wear tracks and wear rate decreased. Finally, depth of strain hardened zone beneath the sliding surface was observed to increase with load.

Friction characteristics of stir-cast Al-Pb alloys

Abstract The coefficient μ of friction of stir-cast Al-Pb alloys with different lead contents and with the same lead content but cast at different agitator speeds against carburized steel has been determined under dry sliding conditions in a Timken wear- and lubricant-testing machine. It is observed that μ remains almost steady with increase in load or sliding velocity for all the stir-cast Al-Pb alloys and commercially pure aluminum but for commercially pure lead it increases sharply with increase in load and sliding velocity. It has also been observed that μ decreases with increase in lead content in Al-Pb alloys until about 20 wt.% but, beyond this composition, it increases sharply. To understand the friction mechanism, the friction tracks are studied by scanning electron microscopy.

The effect of aging on wear characteristics of rheocast-leaded aluminum alloys

In the last few decades, much work has been carried out on leaded aluminum alloys in as-cast condition, but recently, an attempt was made to study the effect of aging on the wear behavior of leaded aluminum alloys. The unique behavior of wear is very similar to the hardness behavior with the aging of partially homogenized Al-Cu alloys investigated earlier. A minimum in bulk wear was observed at about 2 hours of aging. The maximum and minimum in bulk wear are observed to decrease with an increase in sliding velocity. It was also observed that the maximum in bulk wear is attained at lower aging periods.

Wear behaviour of graphitic aluminium composite sliding under dry conditions

Abstract A modified mixing and casting procedure was used for the preparation of Al-1.2 Si-0.8 Fe–Gr composite (wt.%). Graphite and gray cast iron powders were blended and dispersed in Al-1.2 Si matrix alloy melt and poured in a cast iron mould. Gray cast iron powder worked as carrier for graphite particles. The presence of graphite improves the ultimate tensile strength, tensile and compressive stress but beyond 1 % of graphite all properties deteriorate. However, hardness continuously increases and percentage elongation reduces with graphite. In wear studies, different mechanisms: mild-oxidative, oxidative-metallic and severe-metallic, are operative in the different combinations of sliding velocities and applied loads.

Dry sliding wear behavior of Al-SiO2 composites

Abstract Al-base composites with different amount of silica (5, 10, 15 and 20 wt.%) were developed using powder metallurgy route and compacts were sintered at 550 °C for 2 h. XRD analysis of all compositions was conducted for phases and amount of the second phase present. Morphology of the composites shows quite uniform distribution of the SiO2 particles but at higher percentage of SiO2 particles the clustering starts. Mechanical properties such as uniaxial compressive strength (UCS) and hardness were evaluated and it is seen that among all compositions, composite with 10 wt.% SiO2 has maximum UCS and hardness. Wear behavior of all composites was studied with sliding distance, applied loads, sliding velocity and composition. All composites show a linear increase in cumulative wear with distance and load. Wear rate with load increases continuously for all compositions, however, composite with 10 wt.% SiO2 revealed minimum wear rate with distance, sliding velocity and loads. Wear rate with sliding velocity increases sharply after attaining minima at 3 m/s sliding velocity. SEM analysis of wear tracks is in agreement with wear results. Al-10 wt.%SiO2 also shows minimum wear coefficient values for all loads, however, wear coefficient decreases with load for all compositions.

Wear of conventional and experimental aluminium bearing alloys sliding under lubrication

Two compositions of aluminium alloys Al-1.2 wt.% Cu-0.9 wt.% Ni-0.7 wt.% Si and Al-1.1 wt.% Cu were chosen to produce conventional bearing alloys with about 6 & 20 wt.% of tin respectively and other two alloys with same basic compositions were produced using lead as dispersoid in same amount instead of tin. The alloys were prepared by impeller mixing and bottom discharge chill casting technique. Their density, microstructure, mechanical properties were evaluated at room temperature. Sliding wear characteristics of these alloys under lubrication were studied in detail. Debris and worn surface analysis was also done. Tin and lead decreased tensile and compression strength of aluminium matrix alloys, percentage elongation was increased in both the cases. Strength properties of aluminium-tin alloys are slightly more than the equivalent experimental aluminium-lead alloys. Wear rate of leaded alloys is lower than the aluminium-tin alloys. Leaded aluminium bearing alloys exhibit superior wear resistance with slightly lower mechanical properties, to that of aluminium-tin alloys.

Strengthening mechanisms of (Al3Zrmp + ZrB2np)/AA5052 hybrid composites

To establish the correlation between grain size, dislocations, dispersed particles (size and vol.%) along with their solid solution strengthening effects in alloy and combined effect of all on the strengthening of advanced composite materials (Al3Zrmp + ZrB2np)/AA5052 hybrid composites have been selected for the investigation. (Al3Zrmp + ZrB2np)/AA5052 hybrid composites have been synthesized by the direct melt reaction of AA5052 alloy and inorganic salts (K2ZrF6 and KBF4). These composites have been characterised by X-ray diffractometer, optical microscopy, scanning-electron microscopy with energy-dispersive spectroscopy, transmission-electron microscopy, tensile and hardness test. Results indicate the successful formation of second phase reinforcement particles namely Al3Zr and ZrB2 in the AA5052 alloy matrix. Al3Zr particles exhibit rectangular and polyhedron morphology within an average of micron size while ZrB2 show hexagonal and rectangular within an average of nano size. Grain refinement of Al-rich phase observed in the composites, increases with increasing vol.% of reinforcement particles. TEM observation shows the presence of dislocations in the composite matrix which help to improve the strength parameters. Tensile results show the improvement in strength parameters which improve with the increasing amount of particles whereas percentage elongation also improves up to certain vol.% of particles and beyond that decrease. However, bulk hardness shows an increasing trend continuously with vol.% of particles. The strengthening mechanisms, namely dislocation, Orowan, grain-refined and solid solution are quantified for the hybrid (Al3Zrmp + ZrB2np)/AA5052 composites and the total of above are in agreement with experimental results. Solid-solution and Orowan are the predominant strengthening mechanisms in the composites.

Synthesis and tribological properties of AA5052-base insitu composites

Abstract It is important to optimize the properties of a material for a particular application, hence, to find the suitable material for tribological applications, the wear and friction behaviour of AA5052 in situ composites with different kind of reinforcements have been investigated. For present study, three in situ formed composites have been produced with different reinforcements namely Al3Zr, ZrB2 and combination of both (Al3Zr + ZrB2) by direct melt reaction (DMR) technique. The as-cast composites and base alloy have been characterized by X-ray diffraction (XRD), optical microscopy, electron microscopy, tensile testing, hardness and dry sliding wear and friction tests. XRD results indicate the successful formation of second phase reinforcement particles in all composites. Wear test results indicate that the cumulative volume loss increases with an increase in sliding distance while coefficient of friction shows a fluctuating tendency, whereas with increasing applied load, wear rate shows an increasing trend while coefficient of friction shows decreasing trend. The variation of wear rate with composites indicates that the composite with multiple reinforcement (Al3Zr + ZrB2) has lowest wear rate among all as-cast composites and base alloy, while coefficient of friction is higher. The responsible mechanisms concerned with wear and friction results have been discussed in detail with the help of the observation on worn surface analysis by scanning electron microscope (SEM) and 3D-profilometer. All tribological results have been correlated with the microstructural properties, strength parameters and bulk hardness of the composites.