Copper has excellent conductivity, thermal conductivity, corrosion resistance, ductility and certain strength. Adding more than 10 kinds of alloy elements to pure copper (red copper) to form various copper alloys of solid solution, such as adding zinc to brass; Nickel is added as white copper; Adding silicon to silicon bronze; Aluminum is added to aluminum bronze, etc.

Copper and copper alloys can be connected by brazing, resistance welding and other processes, and fusion welding has occupied a leading position in today's developed industry. Welding of copper and copper alloys can be easily realized by using welding rod arc welding, TIG welding, MIG welding and other processes. The process difficulties affecting the weldability of copper and copper alloys mainly include four elements: one is the influence of high thermal conductivity. The thermal conductivity of copper is 7-11 times higher than that of carbon steel. When the process parameters used are similar to those used for welding carbon steel of the same thickness, the copper is difficult to melt, and the filler metal and base metal cannot be well fused. Second, the hot cracking tendency of welded joints is large. During welding, copper and impurities in the molten pool form low melting point eutectic, which makes copper and copper alloys have obvious thermal brittleness and hot cracks. The third is that the defect of producing porosity is much more serious than that of carbon steel, mainly hydrogen porosity. The fourth is the change of welded joint performance. Grain coarsening, plasticity decline, corrosion resistance decline, etc.

 

1. Welding of red copper

The methods of welding red copper include gas welding, manual carbon arc welding, shielded metal arc welding and manual argon arc welding. Automatic welding can also be used for large structures.

 

(1) Butt joint is most commonly used for gas welding of red copper, and lap joint and T-joint shall be used as little as possible. Two kinds of welding wires can be used for gas welding. One is the welding wire containing deoxidizing elements, such as wire 201 and 202; The other is the cutting of general copper wire and base metal, using gas agent 301 as the flux. Neutral flame shall be used for red copper gas welding.

 

(2) Electrode arc welding of red copper. When the thickness of weldment is greater than 4mm, it must be preheated before welding, and the preheating temperature is generally 400~500 ℃. Copper 107 electrode shall be used for welding, and the power supply shall be DC reverse connection. Short arc shall be used during welding, and the welding rod shall not swing laterally. The welding rod can improve the formation of the weld by reciprocating linear movement. The method of gradual back welding shall be adopted for long welds. The welding speed shall be as fast as possible. During multi-layer welding, the slag between layers must be completely removed. Welding shall be carried out in a well ventilated place to prevent copper poisoning. After welding, flat hammer shall be used to knock the weld to eliminate stress and improve the weld quality

 

(3) Manual argon arc welding of red copper. During manual argon arc welding of red copper, the welding wires used are 201 (special red copper welding wire) and 202, and also the red copper wire, such as T2. Before welding, the oxide film, oil and other dirt on the welding edge of the workpiece and the surface of the welding wire must be cleaned to avoid air holes, slag inclusion and other defects. Cleaning methods include mechanical cleaning and chemical cleaning.

 

When the thickness of butt joint plate is less than 3mm, no groove shall be made; When the plate thickness is 3~10mm, V-shaped groove shall be made with the groove angle of 60 º~70 º; When the plate thickness is greater than 10mm, an X-shaped groove shall be made with the groove angle of 60 º~70 º; In order to avoid incomplete penetration, no blunt edges are generally left. According to the plate thickness and groove size, the assembly clearance of butt joint shall be selected within the range of 0.5~1.5mm.

 

Manual argon arc welding of red copper usually adopts direct current positive connection, that is, tungsten electrode is connected to negative electrode. In order to eliminate air holes and ensure reliable fusion and penetration at the root of the weld, it is necessary to increase the welding speed, reduce argon consumption and preheat the weldment. When the plate thickness is less than 3 mm, the preheating temperature is 150~300 ℃; When the plate thickness is greater than 3 mm, the preheating temperature is 350~500 ℃. The preheating temperature should not be too high, otherwise the mechanical properties of the welded joint will be reduced.

 

There is also carbon arc welding of red copper. The electrodes used for carbon arc welding are carbon electrode and graphite electrode. The welding wire used for carbon arc welding of red copper is the same as that used for gas welding. The base metal cutting rod can also be used, and the flux for gas welding of red copper can be used, such as gas flux 301.

 

2. Welding of brass

Brass welding methods include gas welding, carbon arc welding, shielded metal arc welding and argon arc welding.

(1) Gas welding of brass. As the temperature of gas welding flame is low, the evaporation of zinc in brass is less than that in electric welding. Therefore, gas welding is the most commonly used method in brass welding.

The welding wires used for brass gas welding are: wire 221, wire 222, wire 224, etc. These welding wires contain silicon, tin, iron and other elements, which can prevent and reduce the evaporation and burning loss of zinc in the molten pool, which is conducive to ensuring the performance of the weld and preventing the generation of air holes. The commonly used fluxes for gas welding brass are solid powder and gas flux. The gas flux consists of methyl borate and methanol; Flux such as aerosol 301.

 

(2) Welding rod arc welding of brass. In addition to copper 227 and copper 237, self-made electrodes can also be used for welding brass.

 

 

 

 

During the electric arc welding with brass electrode, the positive connection of DC power supply shall be adopted, and the electrode shall be connected to the negative electrode. The surface of weldment shall be carefully cleaned before welding. The groove angle shall not be less than 60 º~70 º generally. In order to improve the weld formation, the weldment shall be preheated at 150~250 ℃. During operation, short arc welding shall be used instead of horizontal and back and forth swing, and only linear movement shall be conducted, with high welding speed. Brass weldments in contact with corrosive media such as seawater and ammonia must be annealed after welding to eliminate welding stress.

 

(3) Manual argon arc welding of brass. Standard brass welding wires: wire 221, wire 222 and wire 224 can be used for manual argon arc welding of brass, or materials with the same composition as the base metal can be used as filler materials.

Welding can be conducted by direct current or alternating current. When using AC welding, the evaporation of zinc is lighter than that of DC positive connection. Generally, preheating is not required before welding, only when the difference of plate thickness is large. The welding speed shall be as fast as possible. After welding, the weldment shall be heated to 300~400 ℃ for annealing treatment to eliminate welding stress, so as to prevent cracks in the weldment during use.

 

(4) Carbon arc welding of brass. During brass carbon arc welding, wire 221, wire 222, wire 224 and other welding wires are selected according to the composition of the base metal, or self-made brass welding wires can be used for welding. Gas flux 301 can be used as flux for welding. Welding shall be conducted with short arc to reduce evaporation and burning loss of zinc.

 

The DC TIG welding process is widely used in the welding of copper and copper alloys. The welding air is well formed, and the internal and external quality is excellent. Under the protection of argon, the molten pool is pure, the porosity is small, the impact of hot cracking is small, and the operation is easy to master. When the thickness is less than or equal to 4mm, preheating before welding is not required, but argon is directly used for preheating. When the temperature of the molten pool is close to 600 ℃, filler wire can be added to melt the base metal to realize welding. For copper with thickness greater than 4mm, the pure copper shall be preheated at 400~600 ℃. Copper alloy welding preheating 200~300 ℃. 300TSP, 315TX DC TIG welding machine can weld pure copper, silicon bronze, phosphor bronze, brass, white copper and other copper alloys. The 300WP5, 300/500WX4 AC/DC TIG welding machine can be used to weld aluminum bronze with AC TIG (remove the surface oxide film with AC square wave) and the above copper materials with DC TIG.

In recent years, more and more copper and copper alloys are welded by MIG method, especially for aluminum bronze, silicon bronze and white copper with thickness ≥ 3mm, MIG welding method is preferred. For copper and copper alloys with a thickness of 3~14mm or more, MIG welding is almost always used. Because of the high deposition efficiency, large penetration and fast welding speed (generally 3~4 times that of TIG welding), the economic benefits of high efficiency, high quality and low cost can be achieved. Before welding, the copper materials shall meet the requirements of preheating temperature (400~600 ℃ for pure copper and 200~300 ℃ for copper alloy). The welding wire shall be chemically similar to the base metal, and the argon purity shall be ≥ 99.98%

 

3. Welding method of stainless steel, copper and its alloys

The main problem of welding stainless steel with copper and its alloys is that the weld zone and fusion zone are easy to produce cracks and penetration cracks in the heat affected zone, especially if the welding filler metal is not properly selected.

 

If austenitic stainless steel is used as the filler metal material, since copper is also an element forming the austenite structure, the weld is still the austenite structure. There is a layer of liquid copper with low melting point between the grains during crystallization, which is easy to cause cracks,

 

When Monel alloy is used as filler metal material (such as Ni70%+Cu30%), due to the high nickel content in the weld, the melting medium of copper in the austenite structure can be increased, the harmful effect of copper can be reduced, and the hot crack tendency can be reduced.

For example, when some copper alloys (such as aluminum bronze) and red copper are used as filler metal materials, due to the high copper content in the weld, there are more copper liquid with low melting point between the austenite grains during crystallization, which has a certain healing effect, so there is less tendency for hot cracks,

 

However, Fe, M, Cr, etc. melted into the weld will make the weld brittle, reduce the impact toughness, and may still produce penetration cracks in the heat affected zone on one side of the stainless steel. Therefore, this type of filler metal can be used only when the mechanical properties of the joint are not required.

 

Because nickel can be infinitely miscible with copper in either liquid or solid state, pure nickel (Ni ≥ 90%, Fe ≤ 8%) is used as filler metal material during welding, which can greatly eliminate the harmful effects of copper, and effectively prevent penetration cracks. It is the best filler metal material.

 

Welding process:

1. Pure nickel is selected as the filler wire, or cast iron electrode Z308 can be used to remove the coating and clean it as the filler wire.

2. Overlay a layer of transition layer on stainless steel or copper (contact welding surface), and then conduct welding.

3. For the welding edges of two workpieces, the oxide layer shall be removed and sanded to bright metal.

 

4. Due to the fast heat dissipation of copper, the nickel electrode arc should be slightly more inclined to the copper side, which is only conducive to good weld fusion.

5. The use of AC power welding can reduce the evaporation of metal melting, especially the welding of stainless steel and aluminum bronze.

6. The welding current can be precisely adjusted according to the thickness and size of the workpiece.

7. Argon flow is 12~15L/min, and high-purity argon is preferred.

 

4. Welding of copper and steel

Method 1: use gas welding and add red copper welding wire.

Method 2: Argon tungsten arc welding with red copper wire.

Method 3: Use J507 welding rod and wrap it outside Φ 1.25 pure copper wire (if it is enamelled wire, it must be cleaned up), baked at 350 ℃ for 2h before welding, and when it drops to 100 ℃, it can be used at any time. Before welding, the workpiece shall be cleaned and preheated with oxyacetylene flame at 650~700 ℃, which shall be maintained during welding. Electrode selection Φ 3.2 mm, the upper limit of current shall be selected, the welding speed shall be 5 ～ 225 px/min, and the DC reverse connection method shall be used for welding.

In order to ensure penetration, the arc stays on one side of the copper plate for a long time, and the arc blowing force is used to fully and evenly mix copper and steel. The winding density is determined according to the thickness of the plate, and the general spacing is 2~3mm. The copper wire cannot contact the welding core and jaw.

 

In principle, copper and most metals are infinitely miscible. Copper wire or brass wire can be used for welding. Take red copper welding for example. Because red copper conducts heat quickly, if your copper plate is thick, the copper plate should be preheated to 200~300 degrees. Gas welding or argon arc welding can be used.

 

As the melting point of the steel plate is nearly 500 degrees higher than that of red copper, the arc first leans to the side of the steel plate during welding, so that the heat of the arc is biased to the steel plate. After the molten pool is formed on one side of the steel plate, the arc is tilted slightly to the side of red copper, and then the welding wire is sent to the molten pool.

 

5. Welding of copper and aluminum

Welding characteristics of aluminum and copper

Aluminum and copper can be used for fusion welding, pressure welding and brazing, among which pressure welding is the most widely used.

 

The main difficulty of fusion welding is that the melting points of aluminum and copper differ greatly (up to 423 ° C), and it is difficult to melt at the same time during welding. Aluminum is strongly oxidized at high temperature, and measures to prevent oxidation and remove oxides in the molten pool shall be taken during welding. Aluminum and copper are infinitely miscible in liquid state, and are limited in solid state. Aluminum and copper can form a variety of solid solution phases dominated by intermetallic compounds, including AlCu2, Al2Cu3, AlCu, Al2Cu, etc. When the copper content in aluminum copper alloy is less than 12%~13% (mass fraction), the comprehensive performance is the best. Therefore, during fusion welding, try to control the copper content in aluminum copper alloy of weld metal not to exceed this range, or use aluminum base alloy.

 

Both aluminum and copper are metals with good plasticity, so they are suitable for pressure welding, especially cold pressure welding, friction welding, diffusion welding, etc.

 

Main welding process points are as follows:

Fusion welding: argon arc welding is preferred for aluminum and copper combination. During welding, the arc center shall be biased to one side of the copper plate, with an offset equal to 1/2 of the thickness, so as to achieve simultaneous melting on both sides. Pure aluminum or aluminum silicon can be used as filler wire. Adding alloy elements to weld metal can improve the quality of aluminum copper fusion welding joint, and adding zinc and magnesium can limit the transition from copper to aluminum; The addition of calcium and magnesium can activate the surface and fill the gap of dendrite easily; The addition of Ti, Zr, Mo and other refractory metals helps to refine the microstructure; The addition of silicon and zinc can reduce intermetallic compounds. The addition method can be applied to the copper surface to be welded before welding.

 

When submerged arc welding is adopted, the joint form is shown in Figure 1. Deviation value of arc and upper edge of copper groove l=(0.5 ～ 0.6) δ，δ Is the thickness of the weldment. The copper side is provided with a J-shaped groove, and the aluminum side is provided with a straight edge. Preset in J-groove φ 3mm aluminum welding wire. When the thickness of the workpiece is 10mm, the welding wire diameter is used φ 2.5mm, wire feeding speed 332m · h-1, welding current 400~420A, arc voltage 38~39V, welding speed 21m · h-1. When the w (Cu) in the weld metal after welding is in the range of 8%~10%, satisfactory mechanical properties of the joint can be obtained.

 

Pressure welding: (1) friction welding. During bar butt welding, the workpiece shall be annealed before welding, the joint surface shall be filed and welded as soon as possible to avoid contamination or re generation of oxide film. The heating temperature of friction welding shall be lower than the eutectic temperature of aluminum and copper (548 ° C), generally controlled at 460-480 ° C. This can not only prevent brittle intermetallic compounds, but also ensure sufficient plastic deformation.

 

Friction stir welding can be used for sheet metal butt welding. As long as the welding parameters are selected properly, good welding joints can also be obtained. Take the butt welding of aluminum alloy 5A06 (LF6)+pure copper T1 with a thickness of 2mm as an example, good weld formation can be obtained when the speed of the stirring head is 375~1180r · min-1, and the welding speed is 30~150mm · min-1. Among them, the joint tensile strength is the highest when the rotating speed is 1180r · min-1 and the welding speed is 30mm · min-1, reaching 297-62MPa, which is 95% of the aluminum alloy 5A05 (314MPa).

 

Another example is quite unique. For 5A05+T2 butt friction stir welding with 4mm plate thickness, the pure copper T2 is placed at the forward side during welding, the stirring pin of the stirring head is 0.9mm away from the aluminum alloy 5A05 side, the preheating is 200 ° C before welding, and the welding is carried out at 1250r · min-1 of the stirring head and 40mm · min-1 of the welding speed, so that good weld formation is also obtained.

(2) Resistance flash welding, energy storage butt welding, aluminum copper flash butt welding and capacitance energy storage butt welding rely on improving the upset speed and sufficient upset force, while strictly controlling the electric upset time, extruding the formed intermetallic compound with the liquid metal out of the interface, making the brittle layer as thin and discontinuous as possible, to ensure that a large plastic deformation occurs at the contact surface. For example, during flash butt welding, high current (twice as much as steel welding), high feeding speed (4 times as much as steel welding), high pressure rapid upset forging (100~300mm · s-1) and extremely short power on upset forging time (0.02~0.04s) are used. Sometimes, in order to prevent the formation of brittle compounds