Cast titanium alloy has a small specific gravity, high specific strength, high corrosion resistance, and good mechanical properties at high and low temperatures. It is an excellent casting structural material and is widely used in the manufacturing of key components for aerospace engines and aircraft fuselage structures. The F-22 fighter jet uses more than 70 titanium alloy precision castings, and 50% of the wings are made of titanium alloy castings. A certain type of aircraft in China also extensively uses titanium alloy hot isostatic pressing castings as the main load-bearing components, ensuring the aircraft’s lightweight, agile, and low-cost performance. ZTC4 is a commonly used backbone titanium alloy in modern aircraft and engine structures among the widely used cast titanium alloys Material Science. During the development of the ZTC4 titanium alloy integral precision casting intermediate casing for a certain thrust to weight ratio engine validation machine and large aircraft engine in China, it was found that there were many defects such as porosity, inclusions, and cracks in the castings. However, important models of aircraft and engines in China urgently need a large number of titanium alloy castings. Titanium alloy castings often have dents that require welding repair after hot isostatic pressing. In addition, the use of castings in aircraft and engines often involves welding with other castings or forged parts. Therefore, the study of argon arc welding and laser welding repair welding techniques for eliminating casting defects in titanium alloy thin-walled castings has important engineering significance and clear demand background.
The base material used in this study is ZTC4 cast titanium alloy sheet, in the state of casting+hot isostatic pressing; Welding materials: Automatic argon arc welding uses φ 1.6TC4 welding wire, manual argon arc welding uses low hydrogen φ 1.0TC4 welding wire, and laser welding uses TC4 powder with a particle size of 150-325 mesh. Study the effect of repair welding frequency on the performance of repair welded joints using ZTC4 automatic argon arc welding repair method. Select 6mm thick ZTC4 titanium alloy sheet and study the influence of repair welding frequency on joint performance. Design a welding repair plan, which first involves connecting two pieces
6mm thick plate butt welding, followed by processing a 3mm to 4mm deep V-shaped groove on the weld seam for repair welding; Then, refer to the previous step to process the weld seam again and perform 2 repair welds. By analogy, a total of 4 repair welds were performed to obtain test plates in 5 states: unrepaired, 1 repair weld, 2 repair welds, 3 repair welds, and 4 repair welds. Perform post weld heat treatment on 5 test plates at 730 ℃ for 2 hours under vacuum. Finally, room temperature tensile and room temperature impact performance tests were conducted on the test plates in five different states to determine the influence of the number of welding repairs on the joint performance. The ZTC4 manual argon arc welding repair method was used to study the effects of pre weld preheating and post weld heat treatment on the performance of repair welded joints. Two specifications of 3mm and 6mm thick plates were selected based on the actual defect situation of the workpiece, and the effects of pre weld preheating and post weld heat treatment on the residual stress and performance of the joint were studied.
(1) Four repair welding tests were conducted on ZTC4 test plates using automatic argon arc welding, and it was found that the tensile and impact properties of the joint at room temperature did not change significantly within the four repair welding ranges.
(2) The residual stress, room temperature tensile and impact properties of joints in four states of welding, preheating welding, welding+heat treatment, and preheating welding+heat treatment were analyzed using manual argon arc welding. The stress state of the base metal is basically compressive stress, while the joints in the welded state are tensile stress, which is also the reason why cracks are prone to occur after welding; After preheating welding, the stress in the Y direction is converted into compressive stress, and the individual tensile stress in the X direction is also reduced compared to the welded state; After post weld heat treatment, the joint stress is basically compressive stress, and some tensile stress values are significantly reduced compared to before treatment. Therefore, welding preheating and post weld heat treatment can effectively reduce welding stress and prevent the occurrence of repair welding cracks.
(3) The room temperature tensile performance of the argon arc welding repair joint reaches over 97% of the base material, and the impact toughness reaches 100% of the base material.