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Why can't aluminum wire and copper wire be connected?

Update:08-05-2020
Summary:

1. The potential of copper and aluminum is different. T […]

1. The potential of copper and aluminum is different. The copper and aluminum contact parts will accelerate the oxidation of the aluminum wire due to the reaction of the galvanic battery. The copper and aluminum joints will be in poor contact for a long time. If you want to connect them together, you must use copper and aluminum excessive clips or excessive conduit.
2. This is a chemical problem. The chemical properties of metals are relatively vivid and non-viable. For example, gold has never been rusted. This shows that gold chemistry is not vivid, iron is simply rusted, and iron is more vivid than gold. Putting the metal together will speed up the oxidation of the vivid metal. Compared with aluminum and copper, aluminum is more vivid. The connection of the two cables will accelerate the oxidation of aluminum (that is, rust) and affect the use.
3. When the copper and aluminum conductors are directly connected, the contact surface of these two metals can easily form an electrolyte under the effect of moisture, carbon dioxide and other impurities in the air, and then form a primary battery with aluminum as the negative electrode and copper as the positive electrode In order to cause galvanic corrosion of aluminum, the contact resistance of the connection between copper and aluminum increases.

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In addition, because the modulus of elasticity and the coefficient of thermal expansion of copper and aluminum are very different, after repeated cooling and heating cycles (power on and power off) during work, a large gap will occur at the contact point and affect the contact, which also increases Contact resistance. The increase in contact resistance will cause the temperature to rise during operation. Corrosion and oxidation will intensify under high temperature, and a vicious cycle will occur, which will further deteriorate the quality of the connection. Eventually, the temperature of the contact point will be too high, and smoke, burning, etc. will occur.

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