Low-temperature Diffusion Welding Of TC4/1060Al Joints And The Defense Ability Of TC4-1060Al Rear Wall

The increasingly frequent space launch activities in the world have led to an increasing number of space debris in orbit.In particular,space debris,which size is below 1cm,is difficult to detect,and the number is large.The existence of these debris seriously affects the safe operation of spacecraft.At present,for the protection of such space debris,a passive protection method is added on the outside of the spacecraft.The commonly used protection structure is based on the development of Whipple protection structure.The stuffed Whipple protective structure is generally composed of a buffer screen,a filling layer and a rear wall.The rear wall materials commonly used in spacecraft are mainly made of light aluminum alloy,which leads to the phenomenon of perforation and spalling of the rear wall material of the current protective structure.There is an urgent need to develop a lightweight and efficient new type of rear wall protection material that meets the requirements of being able to withstand the continuous and discrete penetration of debris clouds.To this end,the paper takes the rear wall material of stuffed Whipple protective structure for space debris protection as research background.We Select titanium alloy TC4 and aluminum Alloy 1060 Al as the research object,meeting the conditions of low density,high specific modulus and specific strength,low coefficient of linear expansion,anti-aging and low outgassing rate under vacuum.The TC4-1060 Al rear wall material was obtained by diffusion welding at low temperature,used in Stuffed Whipple Shields.First of all,Investigations were mainly focused on the influence of the initial contact area(the degree of surface oxidation,the angle between the scratches and the interface roughness)on the microstructures,elemental distributions across the interfaces and mechanical properties of TC4-1060 Al joints,combining numerical simulation research.Secondly,we also analyze and study the performance of the TC4-1060 Al rear wall material against hypervelocity impact and analyze the macro damage and micro tissue of the TC4-1060 Al system rear wall material.Provide a new exploration idea for the design,preparation and performance optimization of anti-high-speed impact materials.The paper firstly controls the initial effective contact area of the sample to be welded by simple orientation grinding and assembly.Under the conditions of 410°C-120min-20 MPa,excellent TC4-1060 Al welding joints are obtained.Studies have shown that the performance and structure of the TC4-1060 Al weldment are affected by the initial effective contact area of the sample to be welded,and the interface to be welded is a Hamilton model of reciprocal bite ridges during the diffusion welding process.The high-strength welding of the TC4-1060 Al weldment is obatained at low temperature,and the welding temperature is much lower than the welding temperature(500-680 °C)of Ti-Al reported in the existing literature.The shear strength of the prepared TC4-1060 Al welded joint first increases with the increase of the roughness of the surface to be welded,and then basically remains unchanged.When the he scratches on the surface of the sample to be welded are parallel to each other,TC4 surface roughness Sa is 109.90 μm and the 1060 Al surface roughness Sa is 101.43 μm,the maximum joint shear strength is 128 MPa.The element diffusion at the interface of TC4-1060 Al solder joints was uniform,and almost no brittle intermetallic compounds were found.The Al element diffuses into the Ti alloy matrix to form a solid solution.The thickness of diffusion layer is about 5nm.The fracture of TC4-1060 Al welded part is ductile fracture,and the fracture failure is mainly at the joint interface near the aluminum alloy side.According to the analysis,when the scratches on the surface of the sample to be welded are parallel to each other,TC4 surface roughness Sa is 109.90 μm and the 1060 Al surface roughness Sa is 101.43 μm,the effective contact area of the sample to be welded is the largest,and the atoms can fully diffuse to the surface to be welded.The ridges of the surface to be welded are fully meshed with each other,and the gaps and holes left between the surfaces before welding can be eliminated during the temperature increase process.The scratches on the original interface can be eliminated during the temperature increase process,and the welding difficulty and temperature are reduced.The TC4-1060 Al welded joints have the best performance and structure.According to the dynamic loading simulation test and isosurface density requirements,the thickness of TC4 and 1060 Al is designed,and the TC4-1060 Al weld joint with good performance under low temperature is used as the rear wall of the stuffed Whipple shields.In the dynamic loading experiment,the anti-penetration performance of the TC4-1060 Al rear wall material is obviously better than that of the aluminum alloy rear wall material with the same surface density.The TC4-1060 Al rear wall did not show any common damage such as perforation and peeling in the collision with the debris cloud.The overall deformation was small,and the deformation protrusion was only 3.5 mm,which was smaller than the aluminum alloy protection board with the same surface density.Under the scanning electron microscope,a small crater can be observed on the impact surface of the titanium alloy.The diameter of the small crater is in the range of several micrometers to several ten micrometers and the depth is several micrometers.The molten particles of the titanium alloy collided with the debris cloud to impact the aluminum alloy,leaving splashes to solidify and form some pores in the crater.The spallation occurs mainly in the aluminum alloy layer close to the side of the titanium alloy.The spalling phenomenon is less in the TC4-1060 Al rear wall material,but the split cracks are thinner than the split cracks in the pure aluminum plate with the same surface density.According to the analysis,the specific strength of titanium alloy is high.After the debris cloud’s shock wave reaches the TC4-1060 Al rear wall,the titanium alloy layer resists the continuous discrete impact of the debris cloud.The shear wave generated in the titanium alloy will propagate for a long time,which will delay the direct impact of the shock wave on the aluminum alloy.And the anti-penetration performance of the TC4-1060 Al rear wall protection plate on the debris cloud can be improved.