1. Overview
The reason for copper and aluminum welding is to reduce costs and reduce weight, because the density of aluminum is about 1/3 of that of copper, and the price is about 1/5 of that of copper, so aluminum is used instead of copper in many occasions, especially It is the power industry, and copper-aluminum welding has also appeared.
However, the surface of copper and aluminum is very easy to be oxidized, especially the oxide film of aluminum is very firm, resistant to high temperature (melting point up to 2050 ° C), and has a large resistance. If the machine is connected, the contact contact is unstable during power operation, and smoke often occurs. , explosion phenomenon, easy to cause serious consequences such as fire.
In general, copper-aluminum welding can be fusion welding, pressure welding and brazing.
2, the difficulties of copper-aluminum welding
1. The welding of copper and aluminum belongs to dissimilar metal (non-ferrous) welding, which is much more difficult than copper-copper and aluminum-aluminum welding.
2. Both copper and aluminum are easily oxidized, and high melting point oxides are formed during the welding process, which makes it difficult for the weld metal to fuse completely, which brings difficulties to welding.
3. The welded joint of copper and aluminum is brittle and prone to cracks. During fusion welding of copper and aluminum, eutectic such as CuAl2 is easily formed in the weld near the copper side, which is distributed near the grain boundary and is prone to intergranular cracks. .
4. The melting point of copper and aluminum is very different. In fusion welding, copper remains solid when aluminum is melted. When copper is melted, aluminum has melted a lot, which increases the difficulty of welding.
5. The welding seam is prone to porosity. Due to the good thermal conductivity of copper and aluminum, the metal in the molten pool crystallizes quickly during welding, and the metallurgical reaction gas at high temperature does not have time to escape, so pores are generated.
3. Introduction of welding method of copper and aluminum
1). TIG welding
① Preparation before welding: a Clean the surface of the copper and aluminum weldments. b. Bevel the brazed parts, and determine the groove form according to the principle of increasing the weld area of the copper side and the copper content in the weld as much as possible. Generally, a U-shaped groove is used, and the aluminum side may not be grooved. c welding materials are Ag65Cu20Zn15, Q203, ER4043. d A set of welding machine WES315 and oxygen-acetylene equipment.
②Welding operation: a. Assemble and fix the copper and aluminum weldments to prevent deformation and displacement during heating and welding. b First braze a layer of high silver solder (about 1mm) on the copper side with oxygen-acetylene flame.
c Use aluminum-silicon welding wire for argon arc welding while it is hot; during the welding process, the center of the tungsten arc is deviated to the side of the aluminum weldment (this is different from the direct tungsten argon arc of copper and aluminum!);
The guiding ideology of its welding process operation: one is to minimize the content of copper in the weld, and the other is to try to braze on the copper side and weld on the aluminum side.
d The inclination angle between the welding torch and the workpiece is usually 75~85º, 90º when starting the arc, and then maintain the normal inclination angle (biased to the aluminum side).
e The length of the tungsten arc is generally about 5mm, and the thinner the weldment, the shorter the arc length.
f Put the filled aluminum welding wire on the edge of the molten pool, and the angle between the welding piece and the weldment is less than 15º. The end of the wire should not be in contact with the molten pool, but it should always be within the argon protection range. Do not lift the aluminum welding wire very high or at an inclination angle. too big.
g The filler aluminum welding wire should be preheated necessary on the arc side, and then fed into the center of the arc to fuse with the matrix to avoid large sections of the aluminum welding wire.
h If the tungsten electrode sticks to the weldment, do not rush to lift the welding torch at this time, you should first release the control switch, and then gently shake the welding torch to make the tungsten electrode separate from the weldment, otherwise the tungsten electrode will be easily broken.
i When there are defects such as craters, cracks and collapses at the end of the argon arc welding head, the filling amount of the welding wire should be appropriately increased at the end of the argon arc welding head, and the argon arc welding technology should be improved in peacetime.
③ Grind to technical requirements after welding.
2). Submerged arc welding
① Generally, the copper side is beveled (usually U-shaped), and the aluminum side is not beveled.
② During submerged arc welding, the arc should point to the aluminum side, and the optimal offset distance is 5~7mm.
③ Elements such as Si, Zn, Ag, Sn should be appropriately added to the weld.
④Example of welding parameters: the thickness of copper and aluminum plate is 10mm; when the aluminum welding straight diameter is ø2.5, and the material is SAl2, the welding current is 400~420A, the welding voltage is 38~39V, and the welding speed is 0.58cm/s.
3). Electronic quick welding
In order to avoid direct electron beam welding, the θ phase of the CuAl2 eutectic structure is formed in the joint after welding and a large amount of η and β phases are added to make the weld metal hard and brittle. Ag is usually used as the intermediate alloy layer. A mutual soluble solid solution is formed, so a good joint is obtained by welding with a thickness of about 1 mm Ag as an intermediate layer.
4). Flash butt welding of copper and aluminum
①Pre-welding preparation: a. The processing of copper-aluminum weldments should be precise and straight in shape. b Clean the surface dirt and oxides. c. Annealing treatment of copper and aluminum welding parts (copper parts at 600~650℃, heat preservation for 40~60min, cooling in water. Aluminum parts at 400~450℃, heat preservation for 40~60min, air cooling) to reduce hardness, increase plasticity, and improve welded joints quality.
②Flash butt welding can extrude brittle intermetallic compounds out of the joint, causing large plastic deformation of the contact surface, and obtaining a better joint, which is one of the important methods of copper-aluminum welding.
③Example of parameter selection of flash butt welding machine (using LQ-200 type): butt welding surface of copper and aluminum welding parts 6×60mm²; extension length Cu29mm, Al17mm; fixture pressure 0.44MPa; upsetting pressure 0.29MPa; firing time 4.1s; live upsetting time 1/50s; cam angle 270º.
5). Friction welding
①Low temperature friction welding (current mainstream friction welding method):
a It is to control the temperature of the friction surface below the copper-aluminum eutectic point temperature of 548 °C, that is, to complete the copper-aluminum friction welding within the temperature range of 460~480 °C. This temperature range is the best range, and satisfactory copper-aluminum welding can be obtained. connector. It belongs to semi-heated pressure welding, and the required upsetting pressure per unit area is smaller than that of cold pressure welding, but larger than that of flash butt welding.
b Example of low temperature friction welding technical parameters selection: copper and aluminum weldment diameter ø10; speed 450r/min; friction time 6s; upsetting pressure 392MPa; maintenance time 2s; 12.6cm/min; pre-welding pre-pressure 490~588N; friction pressure 166~196MPa.
②High-temperature friction welding: a During high-temperature friction welding, the rotational linear speed can reach 0.58m/s, and the temperature of the contact surface can reach the melting point of aluminum (660℃), which completely exceeds the temperature of copper-aluminum eutectic (548℃). At this temperature, the copper and aluminum atoms undergo a diffusion reaction with each other, which can form a good welded joint.
b Preparation before welding: Process the copper end face into a 90º taper angle; fire copper and aluminum weldments; clean up after annealing.
c. Example of high temperature friction welding technical parameters selection: diameter of copper-aluminum weldment ø10mm; rotational speed r/min; outer ring linear speed 0.71m/s; support friction pressure 147MPa; copper shaft angle 60º.
6). Cold pressure welding
The essence of cold pressure welding is to use the workpiece to be welded at room temperature to produce plastic deformation, extrude the oxide film on the contact surface of the workpiece out of the weld, so that the metal atoms between the interfaces reach the distance of the interatomic attraction, accompanied by interatomic diffusion, Creates a strong link between atoms. Mainly suitable for copper and aluminum welding of small and medium sections.
①Butt welding of copper and aluminum:
a Butt cold press welding is carried out at room temperature without any external heating source, the metal structure does not undergo recrystallization and softening annealing, the strength of the joint is not lower than that of the base metal, and the cross-sectional area of the butt joint is in the range of 1~1000mm². Transformers, overhead wires, etc.
b. Example of selection of technical parameters for copper-aluminum butt cold-pressing welding: annealing before welding; straight diameter of copper-aluminum weldment ø10mm; each weldment protruding length: copper 10mm, aluminum 10mm; upsetting forging 3 times; upsetting pressure 333MPa.
②The lap welding of copper and aluminum:
a) Cold-press welding in the form of plate-plate, wire-wire, wire-plate, foil-wire, foil-plate, etc. of copper and aluminum plastic materials, the best joint form is lap joint. Cold spot welding can be performed in a similar manner to resistance spot welding.
The shape of the solder joint indenter is circular: d=(1~2)δ; rectangle: a=(1~2)δ, b=5~6a.
In multi-spot welding, the distribution should be staggered, and the distance between the centers of the welding spots should be greater than 2d.
b. Example of selection of technical parameters for cold pressure welding of copper and aluminum tower connection: size of weldment 40×4mm²; lap length 70mm; number of solder joints 6; pressure point diameter Al ø7, Cu ø8; total length of indenter Al 30mm, Cu 55mm; The point center distance is 10mm; the pressure is 235MPa.
7). Capacitor energy storage welding
①Capacitive energy storage welding is a special form of resistance welding, which belongs to solid phase welding. The essence of energy storage welding is to store energy in a certain form in advance, and then release it through the weldment in a very short time, instantly generating a large amount of thermal energy at the joint, and at the same time forming a welded joint under rapid extrusion. The electrical conductivity and thermal conductivity of copper and aluminum are very good, and the strong specification of high current and short time must be adopted when welding. Capacitor energy storage welding is especially suitable for welding small cross-section copper and aluminum wires. It is an ideal method for welding copper and aluminum wires at present, but its process parameters can be adjusted in a narrow range, so it is necessary to strictly follow the welding process parameters before welding. Produce high-quality copper-aluminum welded joints.
②Example selection of capacitor energy storage welding process parameters for copper and aluminum thin wires: wire diameter Alø1.81, Cuø1.56; capacitance 8000uF; welding voltage 190~210V; extension length Al2.5mm, Cu2.0mm; upsetting pressure 608MPa ; Clamping force 2650N; Transformer ratio 60:1.
8). Vacuum Diffusion Welding
①Vacuum diffusion welding is mainly used to manufacture copper-aluminum joints of refrigeration equipment and power equipment. Its process parameters are controlled very strictly, and its quality is more stable than fusion welding, brazing and flash butt welding.
②Before welding, the surface of the copper-aluminum weldment must be strictly added, ground, re-polished and cleaned, so that the ruler may be smooth and free of any impurities. The copper and aluminum plates are stacked and put into the vacuum chamber. The factors that affect the vacuum diffusion welding of copper and aluminum are: heating temperature; welding pressure; holding time; vacuum degree; surface quality of welding parts, etc.
③Example of selection of technical parameters of copper and aluminum vacuum diffusion welding: when vacuum diffusion welding of copper and ZAl2 hard aluminum alloy with a thickness of 0.2~0.5mm is carried out, the heating temperature is 480~500℃; the holding time is 10min; the pressure is 4.9~9.8MPa; the vacuum degree 1.33×10－²~1×10－³Pa.
9). Brazing
①Medium and low temperature brazing
A Scratch welding: choose HL501 (Zn58Sn40Cu2), the general commercial specification is cast bar 5×20×350mm³, the welding method is very simple, the copper-aluminum weldment is heated to about 300℃, without any flux, try to scrape the weldment , if the solder does not melt, continue heating until the solder fills the seam after scraping.
B M51+M51-F: The brazing temperature of this kind of solder and flux is very low at 179°C. The solder cannot be directly heated during welding. The copper-aluminum weldment should be heated, and the heat of the weldment is used to melt the solder. Heating tools are available. : Electric soldering iron, hot air gun, liquefied gas spray gun, kerosene torch, gasoline torch, oxygen-acetylene torch, etc.
C dip brazing: brazing filler metal (Zn96~98%Pb2~4%), flux is rosin (C20H30O2) and anhydrous sprinkling essence (ratio greater than 1), welding method: copper-aluminum joint coated with rosin alcohol solution Quickly immerse in brazing material at about 440℃ for brazing.
D WE CuAl-Q303: This welding material is a flux-cored copper-aluminum welding wire. The brazing temperature is about 400°C. It has its own brazing powder and organic non-corrosive flux. The brazing powder melts with the metal cladding, and it will quickly break the copper and aluminum metal. The surface oxide film and metal surface tension can prevent re-oxidation. The metal surface is wetted by the solder powder, so that the solder can fill the entire welding seam through capillary action. The operation is simple, and it is generally not necessary to clean up after welding. .
E Introduction of other welding materials: WE53+WE53-F is a solid core welding wire with flux, and the brazing temperature is about 400℃; XR-FC22, XR-FC0215, ER15, E9802, FR301, etc. are flux-cored welding wires, which are more convenient to use.
②, high temperature vacuum brazing
a solder: AlSi12
b Preparation before welding: Press the filamentous brazing filler metal into a 0.5~1mm thick back-shaped sheet; clean up the copper, aluminum welding parts and brazing filler metals.
C Assembly: Use stainless steel plate to assemble and clamp in the order of aluminum-solder-copper, and place them in layers.
D furnace brazing: start vacuuming after entering the furnace; when the vacuum degree reaches 10-²Pa, start the heating device; the heating rate is 10~20℃/min, keep at 150℃ for 5min, 350℃ and 540℃ for 5min each, Then continuously heat up to 624°C, keep the temperature for 6 minutes and then cool down; cool down to below 600°C, turn off the heating device, cool to below 450°C, fill with nitrogen to speed up the cooling rate, and then open the furnace door after cooling to below 100°C.
10). Other welding methods
In addition to the above welding methods of copper and aluminum, explosive welding, ultrasonic welding, etc. can also be used.
