Aluminum control arms are becoming more and more popular on vehicles, as manufacturers try to reduce weight.
Many of these control arms are equipped with a ball joint. Because of the strength needed to perform their duty, these ball joints, like all others, are made of steel. (In the case of MOOG – that would be fine-grain forged steel).
As you may know, steel and aluminum don’t get along too well together – the result is galvanic corrosion. It even gets worse when you throw in a catalyst, like road salt. This corrosion can make it very difficult to remove the ball joint, thus forcing one to replace the entire control arm. Plus this corrosion over time can weaken both the control arm and the ball joint, or introduce additional contaminants into the ball socket. Overall, this corrosion can lead to additional repair cost and vehicle down-time.
To combat this corrosion, MOOG utilizes a Zinc-Dichromate coating (looks like gold plating) or resin coating (almost a flat black color) on the ball joint housing and/or ball stud. MOOG even provides a special nut that will not react with the aluminum surface. These coatings also provide addition salt-spray (or “environmental” protection).
It is important that, when you go to replace the ball joint in an aluminum control arm, you install a component that has the proper coating or material enhancement to prevent galvanic corrosion from occurring down the road. (It is interesting to note that many manufacturers may skip this step to save cost, or because they feel it unnecessary.)