It's easy to write. Let me give you a few examples: Bronze Age, mainly Xia, Shang, Zhou, Spring and Autumn. Bronze has poor plasticity, higher density than iron, heavy vessels and difficult sharpening of weapons. Many other metals, such as tin, zinc and lead, should be added to increase plasticity, and the process is very responsible. Only rich people can use it, which is not convenient for promotion. It is rarely used for farm tools (serfs have money). The iron age, mainly from the Warring States period, was not much at first, because iron ore was more difficult to smelt than bronze, and the melting point of iron was much higher than that of copper. And is more easily oxidized than copper at high temperature. The required furnace temperature is higher. The craft is more complicated, but when the technology is mature, it gradually replaces the bronze ware. Later, it was found that the hardness of iron was related to carbon content and cooling time, which was relatively easy to control. High plasticity. The disadvantage is that it rusts easily. But it has been gradually applied to farm tools. Greatly improved productivity. With enough food, society will develop faster. There are more people who can do mental and literary work without farming. Then modern, mainly in various alloys. For example, steel is an iron alloy with chromium or manganese added, and aluminum alloy is relatively light and not easy to rust. Titanium alloy has high hardness, low density and is not easy to rust. ......

The main anti-corrosion methods are painting and electroplating. Stick a protective film on the surface of iron, or connect more active metals such as iron and zinc. This method is generally used on ships, so that seawater will corrode zinc first, thus protecting iron. This is the method of galvanic cell. Now the most valuable thing to recycle is aluminum, because it is difficult to smelt aluminum from aluminum ore. Heating it to a high temperature of more than 3000 degrees to melt the ore, and then electrolyzing it with a large current to produce pure aluminum, which requires a lot of energy. So if it is recycled, it will save a lot of energy, which is more valuable than other metal recycling. .....

The rest will come out by itself.