Modern bicycles are much more efficient than those built many decades ago. The old ones were made of steel and gears that may or may not have perfectly matched. On one hand, a steel-frame bike is better than no bike. On the other hand, a bicycle made with aluminium sheet or tubes is likely to be lighter and less jarring to ride. Space age materials make manufacturing easier while allowing for a more comfortable ride. 

More information on aluminium sheet

It is important to understand what aluminum sheet is. Technically, it is just an aluminum alloy that has been cast into an ingot and then rolled in such a way that it is both flat, strong, and somewhat flexible. Aluminum has a large crystal structure and does not bend as far as steel, but rolled aluminum has these crystals stretched so that it can bend a little. Think of how flexible aluminum foil is.

Most aluminum sheets have textures because they are used either as tiles or as a surface for shoes to grip. While it is possible to roll aluminum sheets into a tube, cast aluminum might be more suitable for the center of the bicycle frame. There are exceptions. If a bike has many joints, it might be easier to use a tube made from sheets. On the other hand, aluminum thick enough to support body weight might not be easily bent.

aluminum sheets are most likely to be used to create a basket, an accessory, or a nonslip surface for the feet. Aluminum is used precisely because it is strong but easy to melt and cast. An aluminum sheet is thin and used to easily build square or rectangular shapes. Someone wanting to use aluminum sheeting in bicycle manufacture should experiment with the material before finding an acceptable use.

Aluminum sheet does come with many stamped shapes and patterns. A fine rough print might be used to augment the pedals. Most pedals are made with plastic and have solid foot grips even when wet, but a cast aluminum pedal might need extra gripping power near the center. Alternatively, aluminum might be used to create a cup holder or guard on the bike frame. The builder has to choose between beauty and function depending on the application.

A sheet would be more likely used to cover sections of a bike frame. Because aluminum is softer than steel and can be made rough, it might hold a paint finish better. This could be important if every part of the frame needs to be made to look uniform. It is much cheaper to use a solid aluminum frame because less time is used, but sometimes the core of the frame might be a special material. The core might be titanium but covered with aluminum.

It is possible to make a basket with aluminum, but aluminum is not impact resistant unless it is thick. It is more practical to use steel wire for baskets because it retains its shape even after bending a little under impact. Aluminum sheet is more frequently used where ease of welding is required. Since aluminum melts at a low temperature, it is ideal for low-cost welding projects.