| With the environment's expanding worsening and the product exception's increasing from customer, galvanized steel sheet has not all met the challenge of automotive industry, household electrical appliances industry and other civilian industry product. For it has more stronger anti-corrosion property and thermal oxidization resistance than the traditional galvanized steel sheet, the Al-Zn alloy coated steel sheet has much extensive applying and developing prospect in automotive industry and household electrical appliances industry.The spot welding technology of the 0.8mm thickness Al-Zn alloy coated steel sheet which made by one factory in rencent years, has been studied in this paper. The writer has executed the spot welding test by the DZ-63 spot-welding machine, the monograph, and the welding current monitoring instrument, measured the welded spot's shearing resistance and tensile force by the material tensile-testing machine, taken picture for the spot-welded joint by the metallographic microscope, analyzed the welded spot crystal's micro-feature, measured the nugget size, the depth of surface indentation and the nugget height by the microscope, and calculated the penetration ratio.The processing parameters detecting test has been firstly carried out, the test result indicates that the electrode easily bonds to the work piece and often needs trim. Then, the spot welding processing parameters' approximate range to the 0.8mm thickness Al-Zn alloy coated steel sheet has been initially defined.On the base of detecting test, the test procedure has been scientifically arranged by the orthogonal experimental design method. The test has measured 4 important indexes to appraise joint's quality ( namely joint's shearing resistance, the nugget size, the penetration ratio, and the depth of surface indentation) . The effect to the 4 welded spot's indexes from the main processing parameters (welding current, welding time, welding pressure) has been analyzed by the direct-vision analysis method and the variance analysis method, and the optimal processing parameters of 0.8mm thickness Al-Zn alloy coated steel sheet's spot welding is I=9.0KA, F_w=2400N, T=14cyc. The orthogonal experimental result indicates that the welding current affects the Al-Zn alloy coated steel sheet's spot welding quality at the most. To verify the above conclusion, the proving orthogonal trial has been carried out and proves the orthogonal test conclusion, at the same time, the tensile test has been also executed to know joint's plastic property of Al-Zn alloy coated steel sheet, the result indicates it has good plasticity.Generally, joint's quality is appraised by its shearing resistance and the nugget size dimension, joint's shearing resistance and the nugget size dimension (the nugget size, the penetration ratio) must be effectively forecast and monitored to gain good spot-welded joint. Using the orthogonal trial's result data to carry out multi-linear regression, the mathematic model has been built between joint's shearing resistance or the nugget size dimension (the nugget size, the penetration ratio) and the welding current, welding time, welding pressure. Using the mathematic model, it has been forecast to the value of welded spot's shearing resistance and nugget size dimension, then the forecast's accuracy has been proved by test. The result indicates that using suitable spot welding processing parameters, the regression equation's forecast value much approaches to the real measured value and has higher forecast's accuracy.For the welding current has the most extent effect to joint's quality, the writer has carried out curve fitting to the front several turns test's data by the primary curve fitting commands of MATLAB software, and gained the relation curve between the welding current and joint's shearing resistance, the nugget size, the penetration ratio or the depth of surface indentation at the same welding time and welding pressure. The curve visually reflects the welding current's effect to joint's quality. The writer has also analyzed the quality question during spot welding when the welding current isn't suitable.4 turns test has been carried out in the study of Al-Zn alloy coated steel sheet's spot welding technology. Metallographic analysis has been executed to the spot welding joint in the last 3 turns test. The macro metallographic of spot welding joint can visually reflect joint's fusion state, the nugget size and the depth of surface indentation. The metallographic analysis is useful to know the welded spot crystal's micro-feature and the influence of the main processing parameters' change to the welded spot nugget's crystal form.
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