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The weld in Figure 12(a) extends from the riser halfway through the plate, and the weld in Figure 12(b) extends along the entire length of the plate cavity. Note the location of the weld in both figures corresponds to the coolest area at the end of filling, shown in the temperature results of configuration B in Figure 3.The area of least mixing at the front also interfaces in the material trace results in Figure 4 for the B design.


In order to observe the depth of the welds, samples were taken from the affected area and mounted and polished for optical microscopy. However, after sample preparation was complete, the confluence weld was no longer visible on the surface; only apparent porosity remained in the path of the weld area (see Figure 13[a]). The cross section of the sample is shown in Fig-


ure 13(b). Here, the weld is located at the top perpendicular to view, showing no major extension into the depth of the plate, which indicates a complete merging of the metal streams. Areas of porosity occur only near the bottom of the image, which is aligned with the weld location on the top surface.


Surface Analysis Optical microscopy results showed that the welds appeared to be only surface defects. Further analysis within the affect- ed areas was required in order to verify such conclusions.


Three samples from the B plate designated for bend tests- -one within and two away from the weld--were scanned along their entire length to obtain profiles from both loca-


Figure 12. Apparent confluence welds along the length of plate cavity in slow-filled B designs. (a)


(b)


(a)


(b)


Figure 13. Optical microscopy images within weld region illustrating: (a) porosity on the surface normal to the cast surface; (b) the cross section.


International Journal of Metalcasting/Spring 2012 75


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