27-06-2012, 05:19 PM
xEffect of Deformation on Al-ZrO2 Particulate composites during cold upsetting
Particulate composites during cold upsetting.doc (Size: 5.16 MB / Downloads: 47)
Abstract
Work has been initiated to fabricate Al-ZrO2 particulate composites through stir casting technique. Composites with varying percentages of reinforcement’s i.e 2, 4, 6 and 8 % were fabricated in the similar procedure. Composites and pure Al were subjected to cold upsetting with various % of deformations, i.e 10, 20, 30, 40 and 50%. Hardness values were measured after each upsetting and for each composite and also for pure Al. Comparative studies were made among composites and also for pure Al. Results show that improved hardness values with increasing percentage of deformation and also with increasing percentage of reinforcement.
Introduction
Metal matrix composites (MMCs) consist, a pure metal or alloy as matrix material, and the reinforcement as particulates, whiskers or continuous fiber. Metal matrix composites possess some attractive properties which include elevated temperature applications, high transverse strength, high electrical conductivity, superior thermal conductivity, high wear resistance, etc. Depending upon the application in service, a variety of composites with different combinations of matrix materials and reinforcements are being produced through different fabrication methods. These composites are fabricated by the addition of a reinforcement phase to the matrix using one of the following techniques namely powder metallurgy [1]; spray atomization and co-deposition [2-3]; plasma spraying [4,5]; stir casting (compo casting) [6,7] and squeeze casting [8]. MMCs with fiber reinforcements are the initial investigations through suitable processes. Expensive manufacturing cost, anisotropy and restricted secondary processing led to the use of particles/ short fibers / whiskers/ as reinforcements in MMCs. Reinforcing with ceramic particulates extended its applications to a greater adaptability and wide range of properties. Metal matrix composites reinforced with ceramic particles are widely used due to their high specific modulus, strength and wear resistance.
Testing
Composite samples (12mmx 18mm) with aspect ratio (1:1.5) were prepared and were subjected to cold upsetting on Universal testing machine (40 tonnes). Samples both pure Al and composites were subjected to various deformations i.e 10%, 20%, 30%, 40% and 50% at a constant strain rate as shown in fig. Hardness values were measured on each sample using Rockwell hardness testing machine. An average of 4 readings was taken and the consolidated readings were listed in table.1
Conclusions
1. Metal matrix composites are successfully fabricated through stir casting technique.
2. Stirring time, method of stirring, stirrer speed, pouring time are the crucial factors
in producing the above composites.
3. The phenomenon of compositing has been observed in the present study.
4. Increase in hardness has been observed with increase in reinforcement contents.
5. Some results are contradictory for hardness with increase in percentage of deformations and also with increasing reinforcement content.