Joining of higher specific strength materials (e.g., magnesium alloys, aluminum alloys, advanced high strength steel, and carbon fiber reinforced composite polymer) is a technical challenge to widespread of multi-materials lightweight vehicle applications. In particular, physical and chemical incompatibility of each material leads to poor mechanical joint performance. Also, galvanic corrosion of dissimilar material joints is another critical issue that must be addressed as well.
We employed a unique solid-state joining technique, called “friction self-piercing rivet (F- SPR),” to join carbon fiber reinforced polymer to magnesium alloy AZ31B sheet. The local friction heat generated between the rotating rivet and bottom sheet can soften and suppress crack generation on the low ductility material (e.g., AZ31B). The mechanical joint strength of F-SPR specimens was evaluated by lap shear tensile, cross tension, and fatigue testing. Furthermore, we evaluated the corrosion performance of F-SPR joints using ASTM B117 salt fog exposure.
Table 1 summarizes mechanical joint performances of F-SPR specimens. Based on the open literatures, very limited research efforts have been made for particularly joining CFRP to Mg alloys. In particular, the lap shear peak fracture load for F-SPR is higher than the mechanical joint strength found from other joining process (e.g., friction stir joining, ~ 1.5 kN). Cross- tension failure load of 2.81 kN was achieved. Both mechanical testing showed the same failure mode, i.e., AZ31B pullout, indicating strong mechanical interlocking between the rivet and AZ31B achieved by F-SPR process. Fatigue life of F-SPR joints was comparable to the fatigue life of resistance spot welding of AZ3B-AZ31 from the open literature. Joint strength of F-SPR retained above 70% of the original F-SPR strength after 200 hours salt fog exposure. Joining of
such dissimilar materials is of critical concern to achieve lightweight vehicle application for economic and environmental purposes.
TABLE 1 SUMMARY OF MECHANICAL JOINT PERFORMANCES FOR F-SPR SPECIMENS.
Lap shear tensile
Failure load (kN)
F-SPR process was successfully demonstrated for the joining of CFRP and AZ31B. Mechanical joint performances, such as lap shear failure load, cross tension failure load and fatigue life, were higher and/or comparable to other welding techniques. These results supported by the Joining Core Program show potential promise for multi-material joining challenges currently being faced by the auto industry and other transportation sectors.
The author thanked financial support by the U.S. Department of Energy Vehicle Technology Office, as part of Joining Core Program. Oak Ridge National Laboratory (ORNL) is managed by UT-Battelle, LLC for the U.S. Department of Energy under Contract DE-AC05-00OR22725.
Notice of Copyright: This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).