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Why is the aluminum in a tin can harder than aluminum can? What characterizes their different properties?

Aluminum vs. Tin

https://en.wikipedia.org/wiki/Aluminium

Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. It is a silvery-white, soft, non-magnetic and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; it is the third most abundant element after oxygen and silicon and the most abundant metal in the crust, though it is less common in the mantle below.

https://en.wikipedia.org/wiki/Tin

Tin is a chemical element with the symbol Sn (from Latin: stannum) and atomic number 50. Tin is a silvery metal that characteristicly has a faint yellow hue. Tin, like indium, is soft enough to be cut without much force.[8] When a bar of tin is bent the so-called "tin cry" can be heard as a result of sliding tin crystals reforming; this trait is shared by indium, cadmium and frozen mercury. Pure tin after solidifying keeps a mirror-like appearance similar to most metals. However, in most tin alloys (such as pewter) the metal solidifies with a dull gray color. Tin is a post-transition metal in group 14 of the periodic table of elements. It is obtained chiefly from the mineral cassiterite, which contains stannic oxide, SnO2.

With that out of the way. It seems that Tin cans are made of Steel while Aluminum cans are made of Aluminum.

Tin Can vs Aluminum Can

https://en.wikipedia.org/wiki/Steel_and_tin_cans

A tin can, tin (especially in British English, Australian English and Canadian English), steel can, steel packaging or a can, is a container for the distribution or storage of goods, composed of thin metal. Many cans require opening by cutting the "end" open; others have removable covers. Cans hold diverse contents: foods, beverages, oil, chemicals, etc. Steel cans are made of tinplate (tin-coated steel) or of tin-free steel. In some dialects, even aluminium cans are called "tin cans".

https://en.wikipedia.org/wiki/Aluminum_can

Aluminum beverage can with stay-tab easy-opening. Note the can is narrowed at the top to allow for a smaller “end” An aluminum can (British English: aluminium can), sometimes erroneously referred to as a "tin can", is a container for packaging made primarily of aluminum. It is commonly used for foods and beverages such as milk and soup but also for products such as oil, chemicals, and other liquids. Global production is 180 billion annually and constitutes the largest single use of aluminum globally.

Wikipedia has an extensive discussion of containers and packaging.

Hardness

The Moh's scale seems to place Aluminum at a 3 and Steel at a 4. This might be a chemistry question rather than a physics question.

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A separate check suggests that tin is quite soft.

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    $\begingroup$ So your first line confuses me : "Why is the aluminum in a tin can harder than aluminum can? What characterizes their different properties?". Further, you are basically asking for a short course in mechanical properties vs crystal/microstructure. Aluminum is an fcc metal, and steel is a bcc structure (mostly). Forget the 'tin' part - at best the inside was tinned to keep the can from rusting on the inside from, e.g., acidic foods. $\endgroup$
    – Jon Custer
    Commented Jul 29, 2019 at 21:59
  • $\begingroup$ Could you clarify your question? It really is unsure whether your question relates primarily to tin, steel or aluminium. $\endgroup$
    – Paul Childs
    Commented Jul 30, 2019 at 1:30
  • $\begingroup$ "Harder" meaning what exactly ? How do you define this "harder" ? Note that the cans have physically different designs that non-trivially relate to the properties of the can with respect to the application of forces. And food cans are designed to prevent leaks and damage to contents, while beverage cans can to some extent deform and contain pressurized materials, so deal with different forces. $\endgroup$
    – StephenG - Help Ukraine
    Commented Jul 30, 2019 at 1:34

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To summarize: tin cans are not made of tin, they are made of steel. At one time they were tin-plated so that the lead-tin solder that was used to seal them up would stick readily to the steel. Today they have electrically welded seams (and mechanically crimped tops and bottoms) so as to eliminate health hazards from the solder and hence no longer require tin plating; to prevent them from corroding when filled with acidic foodstuff, they are lacquered on the inside.

Aluminum and steel have different crystal structures, grain structures, and (some) ductility mechanisms at room temperature and therefore have different yield strengths, but it should be pointed out that there are hundreds of different steel and aluminum alloys with wildly differing mechanical properties- so without specifying exactly what type of steel and aluminum you are talking about, comparisons between them are almost meaningless.

The differences in properties between aluminum and steel and their various common alloys occupy entire chapters of materials science textbooks, making this forum not the best place to learn this subject. See the classic texts by Van Vlack or Shakelford.

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