Drive shaft tube can made of aluminium alloy and steel but what is the main purpose of it does it serve as a connecting rod from engine power to the rear wheels? i am seeking for a formal answer on this.
The purpose of a drive shaft is to transmit power from the transmission (or transfer case) to the differential. This is their main and only purpose.
A drive shaft can be made from any material which can withstand the twisting force. The three most used materials are steel, aluminum, and carbon fiber. Carbon fiber is a more recent addition to the family and is usually used in high performance applications because it is a lot lighter than the other two materials. Drive shafts (which go from transmission to rear differential) are hollow to save weight. The are also broad (have a broad diameter) to be able to support the torque which is transmitted through them. Aluminum drive shafts will be broader than steel to transmit the same amount of torque. Carbon fiber is its own beast.