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CASTING 101


Weld Repair of Structural Castings T


AMERICAN FOUNDRY SOCIETY TECHNICAL DEPARTMENT


he use of welding to repair porosity in metal parts has been discussed often in casting


circles. Welding is used frequently for cosmetic repair, but its use in structural casting may demand strict in-service performance requirements and des- ignated mechanical properties in the weld regions. Although historically, properly accomplished weld repair has been considered to have little or no effect on the mechanical and physi- cal properties of aluminum cast metal components, some casting purchasers do not allow welding under the as- sumption that it may degrade strength and fatigue properties. AFS conducted research to provide validated data on the effect of weld repair on static and dynamic tensile properties of aluminum castings. Stan- dard test bars were excised from alu- minum castings in welded and as‐cast conditions and mechanical property and fatigue tests were performed. Te castings used in the study were sand cast in aluminum alloy E357 using a standardized melt chemistry, melt cleanliness, melt treatment (all melts were grain refined and silicon modi- fied), pouring guidelines and heat treating process to minimize variations in the cast base metal.


Experimental Procedures One-inch thick plates from the


E357 castings were used. Standard test bars were excised from the casting in two conditions: a full weld condition where the gage section of the test bar specimen was entirely weld metal, and a partial weld condition where the gage section of the test bar contained both weld and base metal. Te radiographic quality level in the designated area of each casting was Grade B or better (per ASTM E155) and the micro- structure of the T6 heat


Table 1. Comparison of Tensile Test Statistics Showing the Effect of Type of Weld Repair Specimen on Tensile Properties


Data Set Statistic Ultimate Strength MPa 0.2% Yield Strength MPa No Weld Mean


340.2


Std. Dev 5.0 High Low


Half Weld Mean


Std. Dev 4.3 High Low


Full Weld Mean


Std. Dev 7.1 High Low


350.3 329.6


340.3


346.1 326.1


340.2


348.2 315.1


treated castings contained well modi- fied silicon morphology. Weld repair using the gas tungsten arc process was accomplished by qualified welders at each of three metalcasting facilities. After welding, repaired castings were heat treated to a T6 condition at a single source, and all castings and test bars were marked so that materials, casting process and metallurgical heat information could be traced.


Testing and Test Results Te T6 heat treated weld repaired


castings were shipped to the testing laboratory, sectioned and machined into tensile and fatigue specimens.


306.9 4.0


317.2 299.9


307.1 3.7


313.0 299.2


308.4 3.3


313.7 302.0


Elong. % 1.94


0.62 3.62 1.16


2.00 0.52 3.47 0.98


1.92 0.55 2.94 0.69


All tensile and fatigue tests were ac- complished at room temperature, and all tensile testing was conducted per ASTM B557 (Table 1). Te fatigue data for the three types of specimens (Fig. 1) are also very similar to each other. However, regression suggests the cast (no weld) specimens are slightly better (longer life) at high stress levels. Te 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 study shows that when us-


ing proper weld repair material and process parameters for aluminum sand castings, presence of a weld repair had little negative effect on either tensile or fatigue proper- ties. Tis study should provide confidence when using proper weld repair for aluminum castings and hold promise for similar results for other materials.


Fig. 1. S-N plots of fatigue data for three types of weld repair specimens of E357-T6 sand castings shows the effect of the type of weld repair on fatigue life.


40 | MODERN CASTING January 2017


Tis article is based on the Effect of Weld Repair on Static and Dynamic Tensile Properties of E357-T6 Sand Castings; Gegel, G.A., Hoefert, D., Hirvela, J., Oehrlein, R.; Transactions of the American Foundry Society 2013, paper #13-1210.


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