Aluminum is a very expensive material to build ca car out of. That why its only used in high end cars like top of the line Audis, Jaguar and Lotus. Also aluminum doen't flex like steel. When exposed to vibration and stress it develops very fine cracks. Not exactly idea for a car body. This is why aircraft are limited to fixed number of lifetime flying hours. The aluminum structure simply loses its integrity with time. Plus I doubt a go-cart could do this.