An alternative to aluminum plate could be steel plate. Steel offers similar properties to aluminum in terms of strength and durability, and it is often less expensive. Additionally, steel has excellent weldability and machinability, making it suitable for a wide range of applications where aluminum is used. However, steel is generally heavier than aluminum, which can be a consideration depending on the specific application. Other alternatives to aluminum plate could include materials such as stainless steel, titanium, or composite materials, depending on the requirements of the application and the desired properties of the material.