Method for preparing bimetal composite plate by stirring friction braze welding

Abstract

The invention discloses a method for preparing a bimetal composite plate by stirring friction braze welding. The method comprises that: a plate with small hardness is used as a covering layer metal plate; a plate with high hardness is used as a base layer metal plate; the covering layer metal plate and the base layer metal plate are horizontally fixed on a working platform surface in a lap joint mode; solders which can generate eutectic reaction with one of the upper/base layer metal plates are preset between the upper/base layer metal plates; a non-needle type cylinder friction device is arranged over the covering layer metal plate; the non-needle type cylindrical friction device is made to rotate and be pressed to be closely contacted with the surface layer of the covering layer metal plate, but not penetrate the covering layer metal plate, and the non-needle type cylindrical friction device rotates in the original position or moves forward along the surface of the covering layer metal plate while rotating; by utilizing frictional heat to melt the solders, the upper/base layer metal plates are both quickly melted in the solders, thereby achieving excellent interface combination; and the excessive solders are squeezed out, and a thin and dense soldering seam is formed, so that the bimetal composite plate is prepared. Compared with the braze welding in a furnace, the method has the advantages of high efficiency, energy conservation, pressure lead-in, unnecessary soldering flux and gas protection and short holding time at a high temperature.

Description

technical field [0001] The invention belongs to the field of welding and relates to a method for friction stir brazing. Background technique [0002] Bimetallic materials are composed of base materials and cladding materials with different materials, and the bonding strength between the two depends on their welding quality. Since the welding between the base material and the cladding belongs to the welding between dissimilar metals, brittle intermetallic compounds are prone to appear at the welding interface. In order to suppress the thickness of the intermetallic compound, a solid-phase welding method suitable for large-area welding is often used. At present, commonly used in the industry are rolling cladding method (also known as calendering method), explosive welding cladding method, diffusion cladding method, etc. The most commonly used ones are the explosive welding composite method and the rolling composite method. The disadvantages of the explosive composite method...

AI Technical Summary

Problems solved by technology

The disadvantages of the explosive composite method are: there are strict requirements on the safety of the environment, management, and operation; there are strict requirements on the qualifications of the production unit, which limits its wide application in general production units; the welding quality of the large edge area is poor, It needs to be removed after welding; poor safety and high noise; it is not suitable for the preparation of small-area plates or the working conditions of small-area welding, and the flexibility is poor

[0006] Brazing in traditional resistance furnaces has the following significant disadvantages (mainly due to poor controllability of metallurgical quality):

[0007] (1) High energy consumption: the main reason is that the heat source comes from the Joule heat of a large current flowing through the heating element (such as molybdenum sheet, graphite, etc.), and the workpiece is indirectly heated by the radiation of the heating element; and the heated area is the entire workpiece , it is impossible to achieve only local heating of the welding zone

In addition, not all the radiant heat of the heating element can be used to heat the workpiece, and the large-area heat dissipation of the water-cooled furnace wall is also an important reason for reducing thermal efficiency

[0008] (2) The heating / cooling speed is slow and time-consuming: the reason is that during the heating process, on the one hand, the workpiece is indirectly heated by the radiation of the heating element, and on the other hand, the thermal inertia of the furnace is large, both of which limit the rapid heating of the workpiece; During the cooling process, the thermal inertia of the furnace is also large, and the workpiece is heated as a whole, both of which make the cooling speed slow

The slow heating / cooling rate prolongs the actual high-temperature residence time of the joint (poor controllability), which tends to cause excessive thickening of the brittle intermetallic compound formed at the interface, and the joint becomes brittle

[0009] (3) Flux, vacuum or argon protection are required: Although these measures are beneficial to break the oxide film on the aluminum surface; improve the wettability of the solder to the aluminum substrate; prevent new oxidation during the brazing process; but will increase Cost of production

[0010] (4) Due to the disordered and uneven macroscopic gap filling flow of molten brazing flux and brazing material (Al-Si), dense defects such as gas inclusions and slag inclusions are formed, and the actual brazing rate is low (such as the brazing rate of aluminum / stainless steel only 60-70%)

[0011] (5) The wetting and diffusion capabilities of aluminum-based brazing filler metals on aluminum and steel are different, resulting in uneven welding of the interfaces on both sides

[0014] (1) Flux and shielding gas are required: increased production costs

[0015] (2) The energy utilization rate is extremely low: the impact of aluminum on CO 2 The reflectivity of laser light is high, and the absorption rate is less than 2%.

[0016] (3) In addition, the equipment investment is expensive, and the life of the laser is limited

[0019] The difficulties of Al / steel lap friction stir welding mainly include the following aspects: (1) The yield strength of steel is high, and at the same welding temperature (generally about 400-500°C), the steel is difficult to soften and deform, which affects the interface more seriously, the direct friction between the harder steel and the stirring head will cause severe wear of the tool (needle)

(2) The difference in the coefficient of linear expansion is large, and the free shrinkage of aluminum during the cooling process is large, resulting in shear stress at the interface (parallel to the interface) and residual tensile stress (perpendicular to the interface) that easily causes the interface to peel off at the edge of the interface.

[0020] Based on the above analysis, in view of the shortcomings of brazing in traditional furnaces (high energy consumption, long heating process, need of flux or vacuum protection) and the shortcomings of high cost of laser brazing (large investment, low energy efficiency, need of flux and shielding gas) ), in order to save energy, heat quickly, and avoid using flux or shielding gas, it is necessary to find a heating method that is direct, fast, and can press the mating surface tightly to prevent air intrusion

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