Discussion on the application of aluminum alloy and steel-aluminum mixed joint technology for body parts

- Apr 02, 2019-

In order to solve the problem of energy saving and consumption reduction, all automobile manufacturers are reducing fuel consumption by reducing the overall body weight. However, it is necessary to ensure the stiffness of the overall structure of the car and improve the safety performance of the car at the same time to reduce weight. Therefore, the whole vehicle factory USES a large number of light and high-strength materials (such as all kinds of high-strength steel, aluminum alloy, magnesium alloy, composite material, etc.) to replace the traditional ordinary steel to achieve weight reduction

Due to its small specific gravity and high strength, aluminum alloy can significantly improve the rigidity of body parts while significantly reducing the weight, so the use of aluminum alloy instead of some steel is the main measure to reduce the weight of automobile manufacturing. When the same mechanical properties are achieved, aluminum is 60% lighter than steel, but when subjected to the same impact, aluminum plate absorbs 50% more impact energy than steel plate. Body is the heaviest part in the automobile, through the introduction of aluminum alloy materials in the all-steel body, to achieve "steel and aluminum body structure", has become the inevitable trend of body parts weight reduction. Aluminum alloy connection and steel-aluminum hybrid connection technology play an important role in parts manufacturing of "steel-aluminum body structure".

At present the body parts aluminum alloy connection process has the aluminum arc welding, the aluminum spot welding, the aluminum stud welding, the friction welding, the laser welding, the pressure riveting, the pull riveting, the spin riveting, the hot melt self-tapping screw connection (FDS), the self-punching riveting (SPR) and so on. In order to solve the problem of electrochemical corrosion on the contact surface of different metals, it is necessary to coat the steel and aluminum parts with structural adhesive before using FDS, SPR and other processes. This paper focuses on the introduction of aluminum arc welding, aluminum spot welding, aluminum stud welding, FDS, SPR these five high

 frequency connection process and application.

Aluminum alloy arc welding
(1) features of arc welding of aluminum alloy
Because aluminum alloy is easily oxidized during welding, aluminum oxide (Al2O3) is generated, which is easy to cause defects such as slag inclusion, incomplete fusion and incomplete welding. The oxide film on the surface of aluminum will absorb a large amount of water, which is easy to make the weld porosity. In addition, aluminum and its alloy linear expansion coefficient, thermal conductivity, welding deformation and stress, easy to crack. Therefore, it is necessary to clean the surface of aluminum arc welding to remove the oxide film on the surface, and protect it from oxidation with high purity argon or argon-helium mixture gas during welding. When tig welding, ac power supply is selected to remove oxide film through "cathode cleaning". In the case of direct dc connection, "cathode cleaning" is not required when large standard gas arc welding is used. In order to prevent the occurrence of thermal crack, the measures of adjusting the composition of welding wire and welding process can be adopted. When the al-mg alloy plate containing more than 3% magnesium is welded, aluminum and magnesium alloy welding wire containing more than 3.5% or more than 5% Mg can be used, which has better mechanical properties and corrosion resistance. Aluminum alloys other than magnesium alloys may also be welded with al-si alloy wire if corrosion resistance permits. When the content of silicon increases, the tendency of hot cracking decreases correspondingly. When the content of silicon increases from 5% to 6%, hot cracking will not occur. Therefore, this kind of welding wire will have better crack resistance, but low plasticity and toughness.Due to the high thermal conductivity and specific heat capacity of aluminum, aluminum alloy with the same thickness will consume more heat than steel. In order to ensure good fusion of welded joints, heat sources with high energy concentration and power density should be used. Therefore, the most commonly used welding methods for aluminum alloy are tungsten inert gas welding (TIG) and melting inert gas welding (MIG). In recent years, a kind of high quality arc welding technology with digital automatic control -- cold metal transition arc welding technology (CMT) has been applied more and more widely.