What metal is Zijin in solar vacuum tube?

At present, the vast majority (about 90%) of solar vacuum tubes in China are using "single target aluminum-nitrogen-aluminum" technology, and a small number of them use "copper-stainless steel-aluminum" technology, such as "three high managers". "Copper-stainless steel-aluminum" technology is expensive. The so-called Zijin is copper at most. To add a joke, many domestic enterprises just have too many concepts to go abroad, which is deeply regrettable. Real high-grade solar collectors are made of pure copper and flat plates, but they are very expensive, and there are no factories in China to make them. Look at this website. Au/, which is the most upscale solar water heater brand in the world, and similar brands such as Rheem and VUOCAN.