Aluminum alloy composite diffusion welding process under low vacuum conditions

0 Preface Aluminum matrix composites have great potential for application in the aerospace, automotive, machinery, and sporting goods due to their superior properties such as high specific strength, high specific stiffness, high wear resistance and heat resistance. It is a high-tech field in today's materials science that is being explored and developed. At present, aluminum matrix composites have been used at home and abroad to process crankshafts, cylinders, bicycle racks, telescope racks, and aircraft landing gear. However, due to the special organizational structure of this material, it is difficult to obtain good joint performance by using an ordinary welding method, and welding is extremely difficult. From the published technical data, the research on the welding property and welding process of this material at home and abroad has progressed very slowly, which has severely restricted the application of this material in production practice.

Under a low vacuum condition, the characteristics and mechanism of the aluminum matrix composites welded by direct diffusion welding and the diffusion welding of the matrix aluminum alloy as the intermediate layer were investigated through a series of tests, and the performance and microscopic properties of different welding processes were analyzed. The impact of the organization is to explore effective processes for achieving high-quality connection of aluminum-based composite materials.

1 Test materials and methods 1.1 Test materials At3p6061A1 aluminum matrix composites were prepared by squeeze casting. The volume ratio of the reinforcing phase AtO; is 30%. The composite material: 2004-06-02 The tensile strength in the annealed state is 225 MPa The differential scanning calorimeter DSC, the liquid, solid temperature interval is 595 ~ 668C The microstructure of the microstructure is shown in Table 1 as the chemical composition of the substrate 6061 Al. A 6061 Al aluminum foil having the same composition as the substrate was used as the intermediate layer.

Table 1 Chemical composition of 6061A (mass fraction, %) 05 balance 12 test method 121 joint processing method The material is processed into a size of 10mmX20mmX50mm for butt welding, and the surface of the joint is processed, the process is: first with acetone The surface is oily, then soaked in 20% Na3H solution and 20% nitric acid solution for 3 minutes, and finally rinsed with clean water and blow dried.

122 Welding process The diffusion welding process is carried out in a vacuum chamber around 1 Pa, and the temperature is measured and controlled by thermocouples and thyristors. During the welding process, the test piece was pressured by a self-made jig, as shown. The fixture was made of high-temperature alloy steel and tempered at 700*C. The spindle is used to adjust the size of the space of the clamped specimen. After the specimen is fixed, it is pressurized by the rotating nut. The workpiece and fixture warm up with the furnace during welding. At room temperature, the initial pressure of the jig to the joint is about 20 MPa. During the heating process, due to the thermal expansion of the fixture, the pressure on the workpiece is gradually reduced. This just makes up for the disadvantage that the strength of the aluminum matrix composite material in the liquid and solid temperature ranges is very low, and it is easily broken under a slightly larger pressure. . Into the heat preservation phase, thermal expansion and contraction stop, so that the joint pressure is maintained at a certain value. After the insulation is completed, the workpiece and the jig are naturally cooled in vacuum, and the clamp shrinks so that the joint pressure rises during the process. image. It can be seen from the figure that more droplets appear at the weld seam and a small amount of small droplets appear on the surface of the specimen.

124 tensile test and microstructure observation After welding using css-2205 electronic universal, joint strength with temperature changes can be divided into three phases.

In the first stage, the substrate did not show a liquid phase at temperatures below 600C. The diffusion welding process at this stage is no different from ordinary solid state diffusion welding. Under the action of a certain pressure, the substrate surface materials that are in contact with each other produce local plastic deformation. From the 123 test temperature, the aluminum matrix composite material is heated to the liquid, There is still some stiffness in the solid two-phase temperature range, and there is a critical temperature range. The microscopic connection behavior of the matrix and the reinforcement phase of the welding joint surface in this interval has changed, and the joint strength has been greatly improved. OLE technology passes information created in an application to another application. The method of creating documents to transfer and share information between applications 'loads the process thumbnail files in Auo CAD into OLE containers in CAPP, and generates craft sketch cards accordingly and saves them to the database.

4 Conclusion Through analyzing the research status of domestic and foreign welding CAPP systems and the actual needs of many domestic large-scale manufacturing companies, the characteristics of tabular welding CAPPs have been summarized, and the Client/Server architecture has been selected.

The organizational structure is divided into three layers, namely product layer, component layer and card layer, and a SQL Server network database is established accordingly.

A design method that separates the process content from the process card format is proposed; the pictures are stored in the database, and the simultaneous management of the text card and the process sketch card is realized; and the bidirectional interface between AutoCAD and the AutoCAD is realized by adopting file format conversion and object link embedding technology. .

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