PSI - Issue 14

Vikas Verma et al. / Procedia Structural Integrity 14 (2019) 68–77 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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2 Experimental 2.1 Materials

In the present investigation cast composites were processed by addition of finer fly ash particles (10 microns) and coarser Al 2 O 3 particles (300 – 400 microns) in Al melt. Commercially available Al 7034 ingot was used for MMC’s casting having following chemical composition Si (0.10%), Fe (0.12%), Mn (0.25%), Mg (2-3%), Cu (0.8-1.2%), Zinc (11-12%), Zr (0.08-0.30%), Cr (0.20%), Al (82.6-86.1%), in weight percent, as determined by ED-XRF

spectrophotometer (make-Fischer, Germany). 2.2 Fabrication of Al-flyash-Al 2 O 3 MMC’s

Al MMC’s were prepared by melting half kg Al ingots in 2.2 kW capacity kanthal wound resistance heating furnace as shown in Figure 1. At 750°C temperature Al melt was stirred at 800 ± 50 rpm by a turbine blade type stirrer driven with 1,440 rpm, 0.5 HP motor. Holding time for Al melt at 750°C is 60 minutes. Since the processing was done in ambient atmosphere, Al gets oxidise and an oxide layer forms at the surface. This oxide layer was broken and dispersed in the matrix via mechanical stirring. Al-fly ash-Al 2 O 3 MMC’s were processed via stir casting technique by reinforcing fly ash and Al 2 O 3 particles in varying weight percentage to the Al melt at casting temperature. Table 1. shows the details of Al-fly ash-Al 2 O 3 MMC’s processed via stir casting. At 750°C temperature slurry was poured in steel die to get solidified. Stirring speed was kept at 800 ± 50 rpm to increase wettability and good bonding between reinforcement with the matrix. Stirring temperature was kept at 620°C where Al is in semi - solid state to have effective wettability. Porosity is generally the prime defect in casting so while pouring the molten metal the pouring rate was kept constant and the bubble formation was avoided. It is being reported that the holding time, holding temperature and stirring speed are the significant variables in processing through stir casting and as the holding time, holding temperature and stirring time increases the porosity decreases (Bhushan et al.,2009; Bhushan and Kumar, 2010). Preheating of the permanent mould was done to remove the entrapped gases from the mould. Uniform feeding of reinforced particles in the matrix was done to avoid clustering of particles which may result in inclusion and porosity defects. The mould was taken to a hydraulic press and 6 Mpa pressure was for 20 sec applied to the mixture in order to reduce the porosity in the composite and improved the bonding force between Al-fly ash Al 2 O 3 particles.

Fig. 1. Schematic diagram of stir casting