**2. Experimental procedure**

**Table 1** lists the chemical composition of the as received ingots. The ingots of each alloy were cut, cleaned and melted in an electrical heated furnace using 6 kg SiC crucibles. The melting temperature was about 750°C ± 5 °C. Degassing was

**115**

**Figure 1.**

*Melt Treatment-Porosity Formation Relationship in Al-Si Cast Alloys*

carried out using a perforated graphite impeller turning at 135 rpm using pure Ar gas (0.492 cubic meter/hr) for about 30–40 minutes. The same impeller was also used as stirrer without gas. Strontium was added in the form of Al-10%Sr master alloy (waffles) whereas grain refiner was introduced as Al-5%Ti-15B master alloy in the form of short rods. It should be mentioned here that the manufacturing of the grain refiner produces Al2O3 which will increase in the amount of porosity. For this reason, the grain refiner in this study was added in the form of short rods (cold

**Alloy Cu Mg Mn Si Fe Sr Ti B** A319.0 3.112 0.0071 0.0005 5.59 0.170 0.0000 0.0105 0.0004 A356.0 0.060 0.314 0.0005 6.21 0.099 0.0001 0.0002 0.0002 A413.0 11.17 0.046 0.218 11.17 0.204 0.0000 0.0652 0.0003

Due to the high affinity of Sr to react with oxygen to form SrO oxides, Sr was added during the last 10 minutes of degassing. As for varying the hydrogen level, small pieces of raw potato were added at the end of degassing, (in this case, Sr was not used) followed by AlScan™ measurement. In addition, reduced pressure test (RPT) samplings were taken from the melts. **Figure 1** shows examples of RPT samples sectioned in half to examine the porosity observed under different melt conditions. In all cases, samples for chemical analysis were also obtained from each

Following melt treatment, the molten metal was poured in L-shaped metallic molds (75 mm × 35 mm × 30 mm). The molds were coated with fine grained boron nitride and were preheated at 450°C **Figure 2**. **Table 2** summarizes the sample codes and their melt treatment whereas **Table 3** shows complete analysis of A356.0 alloy

Samples for metallographic examination were sectioned from the middle of the cast bars (25 mm × 25 mm) and polished following standard procedures [24]. Porosity characteristics were evaluated using a Clemex image analyzer in conjunction with an optical microscope. Measurements were carried out at 100× as shown in **Figure 3**. For each sample at least 100 fields were scanned to enhance the accuracy of measurements. Selected samples were examined using an electron probe microanalyzer (EPMA) equipped with EDS and WDS systems, operating

In order to quantify the effect of melt treatment parameters, hardness measuremnts were carried out on the sample surface shown in **Figure 2** using Brinell hardness testing machine using a 10 mm diameter steel ball and 500 kgf force. For each condition, an average of 8 readings was reported. The samples of A319.0

*RPT test taken from: (a) as received alloy, (b) after degassing, (c) 0.25 ml/100 g H2.*

*DOI: http://dx.doi.org/10.5772/intechopen.94595*

*Chemical composition of the as-received alloys (wt.%).*

rolled) to minimize the presence of such oxides.

melt prior to pouring.

as an example.

**Table 1.**

at 20 kV.

