Anodizing is a process that gives metals a stronger surface. Anodizing is usually done by immersing a metal, for example, aluminum, in a bath filled with sulfuric acid. This bath is an electrolyte and a low voltage electric current runs through this acid bath. The electric current allows for the surface of the aluminum to acquire a thin coating of rust or aluminum oxide. This is the whole process of basic anodizing. But in hard anodizing, the extra step will include the acid bath being cooled to the same freezing point as water, and then the amount of the electrical current is also increased.
Hard anodizing is a metal strengthening process that is usually found in industrial or commercial level applications. It is very seldom used for consumer goods or products. There are some aluminum cookware that are given a hard anodizing treatment but consumers usually prefer regular anodizing because this process offers a durable non-stick surface that is better for cooking. Hard anodizing is a process that produces a thicker layer of aluminum oxide. The thicker coating is able to penetrate holes and other imperfections on the surface in order to produce a more uniform look and texture when compared to anodized aluminum. An aluminum sheet that has undergone a hard anodizing treatment will usually have a dark brown or black surface but other colors can also be made.
Hard anodizing aluminum is a popular building material because it is much cheaper than stainless steel. It is also much lighter. Additionally, machining is also easier with anodized aluminum.