Fig. 5. The graph shows the effect of weld repair on the tensile and yield strength of E357-T6 sand castings.
3
Results and Conclusions
Te T6 heat treated,
weld repaired castings were sectioned and machined
into tensile and fatigue specimens at Westmoreland Mechanical Testing and Research Inc., Youngstown, Pa. Tensile testing was conducted per ASTM B557. Initially, the test speed was a strain pac-
Fig. 6. The graph shows the effect of weld repair specimen type and welding source on % elongation of E357-T6 sand castings.
ing rate of 0.005 in./in./min. (0.127 mm/ mm/min.) until a plastic strain of 0.006 in./in. (0.152 mm/mm) was achieved, at which time the speed increased to a crosshead controlled rate of 0.05 in./in./ min. until failure. Fatigue tests were accomplished per
ASTM E466 in force (load) control em- ploying a constant amplitude sinusoidal waveform at 30 Hz. Tis allowed for the
development of S-N curves at an R-ratio of -1. Load application continued until 107 cycles or failure. Te results of the tensile tests (Figs.
5-6) show: 1. Te presence of a weld repair had little or no effect on ultimate or yield strength of the samples. 2. Similar results were obtained from
weld repaired castings prepared by each of the three weld repair sources. Te statistics for the tensile data
(shown in Table 2) suggest the micro- structures of the three types of specimens are either the same or sufficiently similar to not have a major effect on tensile, yield and percent elongation values. Te fatigue data for the three types of specimens (Fig. 7) also are very similar. However, regression analysis suggests the cast (no weld) specimens are slightly better at high stress levels; the full weld and no weld specimens are about the same life at low stress levels, and the partial weld samples demonstrated the longest fatigue life at low stress levels. Tis suggests either a difference in the microstructure, the geometry of any pores present or the number of pores in the original cast structure of the metal in the weld zone. Samples for metallographic analysis
were removed from the gage section of tensile specimens used to determine the properties of the weld repaired speci- mens. Fig. 8 shows the T6 heat treated microstructure present in a no-weld specimen. Tis microstructure is typical of the fully modified microstructure attained in the castings used for the AFS-AMC Phase IV (CIR), Cast E357 Aluminum Statistical Properties program. In comparison, Fig. 9 shows a microstructure of the weld metal in the weld repair specimens. Te very fine
46 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2013
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