Aluminum alloy is widely used in heat dissipation equipment because of its light and beautiful weight, good thermal conductivity and easy processing into complex shape. There are three main types of aluminum alloy heat dissipation equipment:flat and wide, comb-shaped or fishstick;Radial, branch-shaped outer fins in a circular or elliptical shape. Their common features are:the distance between the fins is short, and a groove is formed between two adjacent fins, and the depth ratio is large;The wall thickness difference is large, and the heat sink is thin, and the bottom plate at the root is thick. Therefore, the design, manufacture and production of the heat dissipation profile are difficult.
Some of the radiator profiles are small in size and symmetrical in shape. Most of the radiator profiles are flat and wide, the shape size is large, some are asymmetrical, and the ratio of groove depth to width between heat sink sheets is very large, so it is difficult to produce them. In order to produce radiator profile smoothly, we need to cooperate with ingot, die and extrusion technology. The alloys used in extruding radiator profiles must have good extrudability and thermal conductivity, such as 1A30, 1035 and 6063. At present, 6063 alloy is widely used because it not only has good extrudability and thermal conductivity, but also has good mechanical properties.
The production of aluminum alloy radiator profile should be based on the quality of ingot, mould material and design, reduction of extrusion pressure and extrusion process.
1. Quality requirements for aluminum ingots
The alloy composition of aluminum ingot should be strictly controlled to ensure the purity of alloy melt. For 6063 alloy, the content of Fe,Mg,Si should be controlled. The content of Fe should be less than 0.2%. The content of Si is generally controlled at the lower limit of the national standard, the content of Mg is 0.45% ≤ 0.55%, and the content of Si is 0.25% ≤ 0.35%. Aluminum ingot should be fully homogenized so that the microstructure and properties of the ingot are uniform and consistent.
The surface of the aluminum ingot is to be smooth without segregation or sand. The end surface of the cast ingot shall be flat and cannot be cut into a step shape or the slope is too large (the cut slope shall be within 3%). because the step shape or the cutting slope is too large, when the heat dissipation section bar is extruded by the flat die, the aluminum ingot is directly contacted with the die if the guide fin is not designed, and the die is first contacted with the die due to the uneven end face of the ingot, so that the stress concentration is generated, the tooth shape of the die is easy to break, Or the discharging is caused to be different, and the phenomenon that the blocking mode or the extrusion molding is not good can be easily generated.
2. Requirements for molds
Because the radiator profile mold is many slender teeth, to bear a lot of extrusion pressure, each tooth must have a very high strength and toughness, if there is a great difference between the properties of each other, it is easy to break those teeth with poor strength or toughness. Therefore, the quality of die steel must be reliable, it is best to use H13 steel produced by reliable manufacturers, or choose high quality imported steel. The heat treatment of the die is very important. In order to be quenched by vacuum heating, it is best to use high pressure pure nitrogen quenching, which can ensure the uniform performance of all parts of the die after quenching. Three tempering should be taken after quenching, so that the hardness of the die can be guaranteed to have enough toughness under the premise of HRC48~52. This is an important condition to prevent die from breaking teeth.
The key to the successful extrusion of radiator profile is that the design of die should be reasonable and the manufacture should be accurate. Generally avoid ingot extrusion directly to the die working belt. For the flat and wide comb radiator profile, a small middle and large diversion die is designed to make the metal flow to both sides, reduce the extrusion pressure on the working belt of the die, and make the pressure distribution uniform. Because of the large wall thickness difference of radiator profile section, it is necessary to keep their difference when designing die working belt, that is, the working belt with large wall thickness should be especially larger, which can be as large as 20mm ≤ 30mm, and the position of tooth tip should break through the routine and minimize the working belt. In short, it is necessary to ensure the uniformity of the flow of metal everywhere. For the flat wide radiator, in order to ensure the die has a certain stiffness, the thickness of the die should be properly increased. The increase of thickness is about 30% ≤ 60%. The manufacture of mould should also be very fine, the empty knife should be symmetrical up and down, left and right, the machining error between teeth should be less than 0.05mm, the machining error is easy to produce partial teeth, that is, the thickness of heat sink is uneven, and even the phenomenon of broken teeth will occur.
For the mature section design, it is also a better method to insert alloy steel die, because the alloy steel die has good rigidity and wear resistance, and is not easy to produce deformation, which is beneficial to the forming of radiator profile.
3. Reduce extrusion pressure
In order to prevent the broken teeth of the die, the extrusion pressure should be reduced as much as possible, and the extrusion pressure is related to the length of the ingot, the deformation resistance of the alloy, the state of the ingot, the degree of deformation and so on. Therefore, the casting rod of extruded heat dissipation aluminum profile should not be too long, which is about 0.6 × 0.85 times of the normal casting rod length. Especially when testing die and extruding the first casting rod, in order to ensure the smooth production of qualified products, it is best to test the die with shorter casting rod, that is, the normal casting rod length (0.4 ≤ 0.6) times.
In addition to shortening the length of the casting rod, the profile section of radiator with complex shape can be considered for the first trial extrusion with pure aluminum short casting, and then extrusion with normal ingot after successful trial extrusion.
Homogenization annealing of ingot can not only make the microstructure and properties uniform, but also improve the extrusion performance and reduce the extrusion pressure, so the ingot must be homogenized annealing. As for the influence of deformation degree, because the section area of radiator profile is generally larger, the extrusion coefficient is generally less than 40, so it has little effect.
4. Extrusion process
The key to the production of radiator profile is the first die test of extrusion die. If there are conditions, the simulation test can be carried out on the computer to see if the working belt of die design is reasonable, and then the die can be tested on the extruder. The first die test is very important, the operator should let the main plunger forward and press slowly under the low pressure below 8MPa, it is best for someone to look after the outlet of the die with flashlight light, and so on, after each heat sink of the extrusion die is evenly extruded out of the die hole, the extrusion can be accelerated gradually. When the extrusion continues after the success of the die test, attention should be paid to controlling the extrusion speed and operating smoothly. The heating temperature of the die should be paid attention to in the production of radiator profile, and the die temperature should be similar to the ingot temperature. If the temperature difference is too large, because of the slow extrusion speed, the metal temperature will decrease, and the phenomenon of die blocking or uneven flow rate will easily occur.
The extrusion technology of radiator profile is not only related to the above factors, but also related to the ability and level of extruder, the degree of automation of rear equipment, the operation skills of workers and so on. Different heat dissipation profile sections should take corresponding measures according to their characteristics, which can not be summarized.
Article editor: Yuefeng aluminum industry, more production technical details refer to www.profiles-aluminum.com