into a single casting for a weight reduc- tion from 12.5 lbs. to 9.2 lbs.


Joining Metals


One of the biggest challenges in designing a multi-material structure is determining the joining methods between parts made in diff erent met- als. Contact between bare aluminum and steel can lead to galvanic corro- sion, so mitigation strategies needed to be devised. Two aluminum-steel joining methods were used in the construction of the MMLV. In the traditional method used, an ad- hesive/sealant electrically isolates the materials (typically galvanized steel panels and hard-coat anodized aluminum casting surfaces) prior to being joined using self-piercing rivets. T e protruding end of the rivet also is sealed. Afterward, the assembly is submerged in a phosphate bath and e-coated. In the alternative method,


the steel components are e-coated and the aluminum castings are hard coat anodized before the adhesive is applied and the parts are connected with self-piercing rivets. In this case,


a phosphate and e-coat treatment is not required after assembly. “Going to an all-aluminum vehicle


structure is expensive,” Conklin said. “But with a bimetallic structure, every


The MMLV kick down rail replaced fi ve steel stampings and is about 25% lighter.


Sept/Oct 2015 | METAL CASTING DESIGN & PURCHASING | 23


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