7039 aluminum alloys are widely being used in the aerospace, automotive and defense industries in which welding technique is used for their joining. The main problem encountered during the welding of 7039 aluminum alloy is hot cracking. The aim of this study is to understand the effect of welding parameters on the hot cracking behavior of 7039 aluminum alloy by using Modified Varestraint Test (MVT) with Gas Tunsgten Arc Welding (GTAW) technique. During tests, welding speed was selected as varying parameter, welding current was kept constant and to understand the effect of filler materials 5183 and 5356 aluminum alloy filler materials were used. It has been observed that with the change in welding speed hot cracking susceptibility of 7039 aluminum alloy changes. The effect of filler materials is found to be favorable by decreasing the hot cracking susceptibility of 7039 aluminum alloy. Filler material additions also improved the hardness of the weld metal. Based on the cracking mechanism hot cracks were investigated as solidification cracks and liquation cracks. It has been experienced that liquation cracking susceptibility of the filler material added samples has been affected from the magnesium and manganese contents of the weld seams. Effect of solidification range on liquation cracking was also justified with differential thermal analyses. With the micro examinations the intergranular structure of hot cracking is revealed. In addition, the characterization and growth properties of the hot cracks under cyclic load were tried to be understood and the fractography of these cracks were taken.

Hot cracking is a serious problem that encounters during welding of aluminium-magnesium alloys. In the present study, solidification and liquation type of hot cracks in weld metal and the heat-affected zones of 5086-H32 aluminium alloy were investigated by using Modified Varestraint Test (MVT) with TIG-AC and TIG-DC welding. With determining the size, type and number of cracks, a relation was established between welding line energy and strain on the hot crack formation. This information was used to determine the hot crack safe parameter ranges. The hot cracking tendency as a function of applied parameters were discussed in the frame of temperature fields around the moving heat source. Moreover, the characteristic hot crack locations on the 5086-H32 MVT specimens were generalized. The results of the study indicated that the increase in line energy and strain increased the hot cracking tendency of the specified aluminium alloy. In the low line energy range, the main hot cracking mechanism is the solidification cracking which could be overcome by the use of a suitable filler material. At high line energy range, due to the increased amount of interdendritic liquid, the amount of solidification cracking decreases by healing mechanism. However, because of the enlarged-temperature-field around the weld zone, fraction of HAZ cracking increases. The comparison between the hot cracking tendencies in low and high line energies indicates that the low line energy ranges with low augmented strains resulted in hot crack safer parameters.

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