Analysis of the causes of spot corrosion of LED aluminum profiles

The main factors that affect the spot corrosion of LED aluminum profiles include the alkali cleaning temperature and alkali cleaning time during the pretreatment process, the Zn, Fe, and Si element contents in the alloy composition and the extrusion state of the alloy. Among many factors, the extrusion state of LED aluminum profiles plays a key role, which is related to the distribution of Zn, Fe, Si and other elements that have a greater impact on corrosion performance, as well as the precipitation location of particles such as compounds between metal bonds. In the thick extrusion stripe area, the distribution of spot corrosion has obvious directionality, because the resistance is greater when extrusion in this area, the stress is concentrated here, and the metal lattice is severely distorted and becomes a local high free energy. area, which nucleates preferentially during the subsequent recrystallization process. In order to reduce the interface energy and maintain a stable state, the grains here not only grow abnormally, but also the Mg2Si anode phase, free Si, FeSiAl, FeAl3 and other cathode phases preferentially precipitate, providing the basis for subsequent The conditions for spot corrosion are created.

Due to the above reasons, a deficient area of ferrosilicon element appears near the grain boundary where free Si, FeSiAl, FeAl3 and other intermetallic compounds are precipitated. This area is almost pure aluminum, and the potential is negative, which is the anode. It and the intermetallic compound (the cathode) A microbattery is formed. Under the action of the corrosive medium, the Si and Fe-poor areas (the anode phase) around the cathode phase (such as free Si, FeSiAl, FeAl3) in the microbattery are preferentially dissolved, and Mg2Si also dissolves, resulting in the anode phase. The dissolution of the surrounding Al forms corrosion pits with residues, while the dissolution of the anodic phase forms corrosion pits without residues. When the corrosion conditions continue to deteriorate (such as temperature rise, long alkali cleaning time, etc.), the matrix Al continues to dissolve and the corrosion pits develop in a deeper direction, so the surface morphology appears as some corrosion pits with residues and some The corrosion pits without residues constitute the spot corrosion of LED aluminum profiles mentioned earlier.

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