A method for improving the quality and mechanical properties of 7xxx aluminum alloy friction stir welded joints

A friction stir and aluminum alloy technology, applied in furnace types, furnaces, heat treatment furnaces, etc., can solve the problems that the cooling rate is difficult to reach the critical cooling rate of the alloy, the quality of the welding joint is difficult to control, and the efficiency is low.

Inactive Publication Date: 2017-03-01
CENT SOUTH UNIV
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  • Application Information

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Problems solved by technology

[0005] 7XXX series high-strength aluminum alloys have a high cooling rate when water-cooled after friction stir welding, which can increase the number of solute atoms retained in the aluminum matrix, but it is easy to generate thermal stress, defects, uneven weld structure and performance, and difficult to control the quality of welded joints ; When air cooling is used, the cooling rate is low, the appearance quality of the weld is good, and there is no defect, but the obtained cooling rate is often difficult to reach the critical cooling rate of the alloy, and the number of solute atoms retained in the aluminum matrix is ​​small, so it is difficult to improve the mechanical properties of the subsequent aging treatment provide a good organizational basis
Therefore, the processing cycle is long, the efficiency is low, and the strength of the welded joint is limited by this method.

Method used

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  • A method for improving the quality and mechanical properties of 7xxx aluminum alloy friction stir welded joints
  • A method for improving the quality and mechanical properties of 7xxx aluminum alloy friction stir welded joints
  • A method for improving the quality and mechanical properties of 7xxx aluminum alloy friction stir welded joints

Examples

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Effect test

Embodiment 1

[0022] In this example, friction stir welding is carried out on 7XXX aluminum alloy plates in T6 state after 1.8 mm. After welding, they are cooled with room temperature water and 10% PAG solution respectively. The rate was 1 °C / min. Such as figure 1 As shown, the welded joint cooled by water at room temperature is prone to defects and has poor appearance quality, while the welded joint cooled by 10% PAG solution has no defects and beautiful appearance quality, as figure 2 .

Embodiment 2

[0024] In this embodiment, friction stir welding is performed on a 1.8 mm thick T7-state 7XXX aluminum alloy plate (chemical composition is listed in Table 1). After welding, one plate is air-cooled and then subjected to natural aging treatment; the other plate is processed by the method of the present invention, that is, after welding, it is cooled with a 10% PAG solution, placed in a 45°C environment for 240h, and then heated to 0.25°C / min. 110°C, keep warm for 4h, then take it out and cool it naturally in still air. Test and compare the Vickers hardness of the weld zone, such as image 3 It is shown that the method of the present invention can increase the hardness of the weld zone, especially in the nugget zone and the thermal-mechanical-affected zone, thereby improving the mechanical properties of the welded joint.

[0025] Table 1 Chemical composition of 7XXX series aluminum alloy sheets in T7 state (wt%)

[0026] element Zn Mg Cu Zr mn Fe Si T...

Embodiment 3

[0028] In this example, the 2.5 mm thick T4 state 7XXX aluminum alloy plate is subjected to friction stir welding. After welding, the PAG solution with a concentration of 5% and air cooling are used respectively, and then the natural aging time is different or the temperature is slowly raised after being placed in a 60°C environment for different times. To 121°C, the heating rate is 0.4°C / min, and finally test the tensile properties of the welded joint at room temperature. Table 2 shows the chemical composition of the alloys. Table 3 shows the room temperature tensile properties of the welded joints after different treatments.

[0029] The method of the invention can not only significantly improve the strength of the welded joint and ensure higher elongation, but also greatly shorten the follow-up processing time and improve production efficiency.

[0030] Table 2 Chemical composition of 7XXX series aluminum alloy sheets in T4 state (wt%)

[0031] element Zn Mg...

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Abstract

The invention discloses a method for improving the quality and mechanical property of a 7XXX aluminum alloy stirring friction welded joint. The method comprises the following steps: firstly performing stirring friction-welding on a 7XXX series aluminum alloy, cooling to room temperature by using a PAG solution with concentration of 5%-10%; placing the 7XXX aluminum alloy stirring friction welded joint in the environment of 40-80 DEG C for 2h-8640h; slowly warming the 7XXX aluminum alloy stirring friction welded joint to 100-160 DEG C, keeping temperature for 2-36h, and naturally cooling to room temperature. The cooling process control and the subsequent ageing process of the 7XXX series aluminum alloy after stirring friction-welding are combined, the welded joint quality is improved, the status of precipitated strengthening phase in the welded joint is effectively regulated and controlled, and the mechanical performance of the welded joint is improved.

Description

technical field [0001] The invention relates to a method for improving the quality and mechanical properties of 7XXX ((Al-Zn-Mg-(Cu))) high-strength aluminum alloy friction stir welding joints. [0002] technical background [0003] The 7XXX series (Al-Zn-Mg-(Cu)) high-strength aluminum alloy is a typical age-strengthened alloy, which has the characteristics of high specific strength, good toughness, corrosion resistance and excellent processing performance, and has been widely used as an aeronautical Structural materials in aerospace, transportation and other fields. These alloys often need to be joined in practical applications. The use of traditional fusion welding methods such as MIG is very easy to burn out alloying elements, prone to defects such as hot cracks and pores, and the performance of the welded joint is poor, so these alloys are generally considered unweldable. Friction stir welding technology is a solid-phase joining method, which avoids the series of defec...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C22F1/04C21D9/50
Inventor 刘胜胆陈彬戴芸王绍玲黄璜郑英邓运来张新明
Owner CENT SOUTH UNIV
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