Introduction of Electrochemical Corrosion Properties of Zn-Al Solder for Copper-Al BrazingAt present, the solders commonly used in the brazing of aluminum/copper dissimilar materials include Al-Si series, Zn-Sn series and Zn-Al series solders, among which Zn-22Al solder is a promising solder for aluminum/copper welding....

Introduction of Electrochemical Corrosion Properties of Zn-Al Solder for Copper-Al Brazing

At present, the solders commonly used in the brazing of aluminum/copper dissimilar materials include Al-Si series, Zn-Sn series and Zn-Al series solders, among which Zn-22Al solder is a promising solder for aluminum/copper welding. The solder can significantly improve the spread ability of the solder and the strength of the welded joint. When using Zn-22Al solder to weld copper/aluminum pipes, the joint has good sealing connection performance, which can fully meet the requirements of copper/aluminum pipe welding in the refrigeration industry. Require. Common types of corrosion in copper/aluminum joints are: pitting, stress corrosion, corrosion fatigue, atmospheric corrosion, etc.

The raw materials of the solder are zinc (99.99% purity), aluminum (99.7% purity), aluminum silicon (11% Si) and magnesium (99.95% purity).

Electrochemical Corrosion Properties of Zn-Al Solder for Copper-Al Brazing

The corrosion rates of Zn-22Al-1.5Si alloys with Mg addition are higher than those of Zn-22Al-1.5Si alloys without Mg addition. After observation, large black corrosion pits appeared on the surface of the Zn-22Al-1.5Si alloy without Mg addition, and the surface of the alloy lost its metallic luster, rough, and covered with a layer of loose corrosion products, while the Zn-22Al alloy with Mg was added. -1.5Si alloy showed smaller corrosion pits. Studies have shown that the addition of Mg element can increase the corrosion current density of the Zn-22Al-1.5Si alloy, thereby effectively inhibiting the active dissolution of the anode, and improving the intergranular corrosion, exfoliation corrosion and stress corrosion resistance of the alloy. It can be seen that the addition of Mg element can improve the electrochemical stability of Zn-22Al-1.5Si alloy.

With the increase of Mg content, the corrosion potential value of Zn-22Al-1.5Si alloy does not change much, but it decreases greatly without Mg addition. Obviously, the addition of Mg element improves the corrosion resistance of Zn-22Al-1.5Si alloy, and the addition of 0.03% Mg element makes the Zn-22Al-1.5Si alloy have the best corrosion resistance.

Shear strength of each brazed copper/aluminum lap joint

Solder without Mg addition has the highest shear strength. The weld structure of the sample without Mg addition is finer, and there is no massive aluminum-copper intermetallic compound. This phase structure greatly improves the mechanical properties of welded joints. In addition, the solid solubility of magnesium in zinc is very low, and its solubility is only 0.1% at 368 °C, and Si can easily react with Mg to form Mg2Si compounds and form Mg-Mg2Si binary eutectic. With the continuous increase of magnesium content in the alloy, the microstructure of the alloy also changes.

, in which the irregular bulk Mg2Si phase increases continuously. The presence of Mg2Si phase will adversely affect the mechanical properties of the alloy. Mg2Si is a hard and brittle phase. With the increase of Mg content, the granular Mg2Si phase gradually increases, and the hardness of the alloy also increases. However, the Mg2Si phase itself is a hard and brittle phase, and it exists in the structure in an irregular block shape, which is easy to cause stress concentration, which makes the alloy brittle; The role of crack source will reduce the ductility of the alloy. Therefore, with the increase of Mg content in Zn-22Al-1.5Si solder, the shear strength of Cu/Al sheet welded joints decreased gradually.