Abstract. In the present work, the spray formed a disk of the Al-6Si-20Pb alloy was characterized before and after cold forging process for different thickness reduction. CharacterizationG1 like microstructure and hardness has been done for different location of spray formed a disk. G2 The microstructure of spray formed Al-6Si-20Pb alloy exhibited equiaxed grains of primary Al with the uniform dispersion of ultra-fine particles of lead and globular silicon particles in Al-matrix. After cold forging, grains were elongated perpendicular to the direction of forging and hence aspect ratios of grains are changed. After uniaxial cold forging, it has been found that the hardness was improved. Hardness is increased in the same manner at every section in the disk as before forging. After forging the value of hardness is becomes double.
Keywords: Spray forming; cold forging; Al-6Si-20Pb alloy; microstructure; Hardness.
Aluminum-Silicon alloys meet many of the service requirements because they have such properties high strength to weight ratio, excellent corrosion resistance, good bearing qualities and lower expansion characteristics, but they have poor wear resistance because of their poor lubricating conditions. From the last some years, to overcome the problem of poor lubrication, solid lubricant type of material like graphite, lead (Pb) and silicon carbide etc are used and hence the applications of these materials increased in a large scale. The suitable techniques, spray forming have been developed to disperse such solid lubricants in an aluminum-matrix 2.
The spray forming process essentially combines two steps first atomization and second spraying of a molten metal with the consolidation and compaction of the spray on a substrate 1. It is a new metallurgical process for producing the products having near-net shape with enhanced mechanical properties. Spray Forming process has the main disadvantage is porosity that can be eliminated by mechanical processing like Rolling and Forging.
In the present investigation, Al-6Si-20Pb alloy has been processed by spray forming process in the form of a disk and then cold forgedG3 . The change in microstructure and hardness of the different location of spray formed material are reported for the different percentage reduction in thickness.
Spray forming process
A schematic of spray forming set-up is shown in fig. 1. The desired amount of charge (Al-6Si-20Pb) was melted in a crucible at the temperature much higher than melting temperature of aluminum so as to provide superheat. The heating was carried out for about 1 hour. A stopper rod runs through the centre of the charge and centre and locates in the top of a delivery tube at the base of the crucible. The thermocouple in the centre of the stopper rod allows continuous measurement of the charge temperature. When a predetermined temperature is reached, the high-pressure nitrogen gas flow is started through the atomizer assembly, the stopper rod is raised and the molten G4 metal flows through the delivery tube. The molten metal stream exits into the deposition chamber and is atomized into variously sized droplets by the impinging energetic gas stream. Atomized droplets are collected over a rotating copper substrate which was either inclined to 0°, 15 or 30 from the central axis of the atomizer to achieve a disk shape preform. Deposition is complete when the metal flow is exhausted. The details of the process variables used in the present study are provided in table 1.