**2. Experimental procedure**

The present work was divided into two parts: stage I aiming at evaluating the effect of metallurgical parameters on the residual stress in B319-based alloys and stage II measuring the residual stresses in I-4 and V-6 engine blocks using the information gathered from stage I.

#### **2.1 Stage I**

The chemical composition of the B319.1 base alloy coded E is shown in **Table 3**. The as-received ingots were melted in a 120-kg capacity SiC crucible, using an electrical resistance furnace. The melting temperature was maintained at 750 5°C. Both alloy melts were grain refined and modified using Al-5% Ti-1%B and Al-10% Sr master alloys, respectively, to obtain levels of 0.25% Ti and 200 ppm Sr in the melt. Finally, the melts were degassed for 15–20 min with a rotary graphite impeller rotating at 130 rpm, using pure dry argon. Following this, the melt was carefully skimmed to remove oxide layers from the surface.

The melt was poured into different molds for various purposes, namely (a) ASTM B-108 permanent mold, for preparing the tensile test bars; (b) an L-shaped rectangular graphite-coated metallic mold; and (c) a block shaped graphite-coated metallic mold. All molds were preheated to 450°C to drive out moisture and avoid cold shut of the blocks. Regarding ASTM B-108 mold, each casting provides two test bars, with a gauge length of 70 mm and a cross-sectional diameter of 12.7 mm. Three samplings for chemical analysis were also taken simultaneously at the time of the casting; this was done at the beginning, in the middle, and at the end of the casting process to ascertain the exact chemical composition of each alloy.

The L-shaped mold and block castings were mainly used for residual stress measurements and microstructure samples and for preparing samples for microstructural examination. The molds were preheated to 250°C. Samples were prepared for the measurement of secondary dendrite arm spacing (SDAS) and grain size in both alloys. Bars were cut from both molds with the dimensions of 200 40 40 mm<sup>3</sup> for measuring of residual stresses using the sectioning method. All the samples, tensile test bars for residual stress measurements treated. Tensile test bars were to the point of fracture using a servohydraulic mechanical testing machine (model 801 produced by MTS), at a strain rate of 4 <sup>10</sup><sup>4</sup> <sup>s</sup> 1 .

Samples for microstructural characterization were used for secondary dendrite arm spacing (SDAS) and grain size measurements. For grain size measurements,


#### *Advanced Applications of Hydrogen and Engineering Systems in the Automotive Industry*

*Generation and Relaxation of Residual Stresses in Automotive Cylinder Blocks DOI: http://dx.doi.org/10.5772/intechopen.93664*


#### **Table 2.**

*Aluminum foundry and die casting alloys (standard and custom specification aluminum ingots).*

#### **Figure 3.** *Origin of residual stress formation.*


### **Table 3.**

*Chemical composition of the B319.1 alloy.*

the polished samples were etched for 15 seconds, using a solution containing 2 ml HF (48%) + 3 ml HCl (conc.) + 5 ml HNO3 (conc.) and 190 ml distilled water.

Residual stress measurements using the sectioning technique require block surface preparation and strain gauge installation prior to strain measurement and calculation of residual stress.

