Through years of research, we have concluded the best materials for use in magnetic sweeper manufacturing to be aircraft grade aluminum extrusions. The most durable, lightweight form of extrusion for this purpose is a 6063 T-5 Aluminum. This aluminum is extremely lightweight, exceptionally hard and will withstand all weather environments. Magnetic Sweepers tend to be subject to road/surface impact and this grade of aluminum will handle impact, abrasion and surface contact with barely a scratch or dent.
The main reason that many manufacturers use the lesser grade aluminum and steel housings is the cost. These cheaper housings tend to be about 20-30% less however their lifespan and effectiveness is equally less. A magnetic sweeper assembled with the high grade 6063 T-5 aluminum will last indefinitely as there is no environmental cause for degradation.
When shopping, always be sure to ask what the specific housing construction is. If the seller/vendor cannot answer, stay clear.