Joining of Dissimilar Automotive Materials

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1 Joining of Dissimilar Automotive Materials P.K. Mallick William E. Stirton Professor of Mechanical Engineering Director, Center for Lighweighting Automotive Materials and Processing University of Michigan-Dearborn Dearborn, MI /3/2015 PKM 1

2 Outline Dissimilar Materials in Automotive Body and Chassis Applications Joining Options Material Properties to Consider for Joint Evaluation Joint Evaluation Methods Adhesive Joints 4/3/2015 PKM 2

3 Automotive Materials Scenario Automotive Body Structure/Frame and Chassis Members/ Body Panels/Seat Structure etc. Steels (Stamped/Roll Formed) Aluminum Alloys (Stamped/Cast) Magnesium Alloys (Cast) Sheet Molding Compounds (SMC) (Compression Molded) Thermoplastics and Thermoplastic Matrix Composites (Injection Molded and Compression Molded) Carbon and Glass Fiber-Epoxy Composites (RTM) 4/3/2015 PKM 3

4 Automotive Materials Scenario Mercedes-Benz CL (2004) 4/3/2015 PKM 4

5 Current and Future Materials Steels Al Alloys Mg Alloys Thermoplastics Thermoplastic Matrix Composites DQ AA 5182 AZ 91 PP SFT SMC IF AA 5454 AZ 31 ABS LFT GFRP BH AA 5754 AZ 80 PA-6 GMT CFRP HSLA AA 6009 PA-66 DP AA 6016 PC TRIP AA 6061 PET TWIP AA 6111 PBT Boron Thermoset Matrix Composites 4/3/2015 PKM 5

6 Joining Options for Metals Liquid Phase Welding Resistance Spot Welding Gas-Metal Arc Welding etc. Laser Welding Solid Phase Welding Friction Stir Welding (FSW) Friction Stir Spot Welding (FSSW) Magnetic Pulse Welding Mechanical Joining Bolting Screwing Self-Piercing Riveting (SPR) Brazing Ultrasonic Welding Clinching Adhesive Joining Adhesive Bonding Weld-Bonding Rivet-Bonding 4/3/2015 PKM 6

7 Joining Options for Plastics and Composites Thermoplastics and Thermoplastic Matrix Composites Vibration Welding Ultrasonic Welding Resistance Welding Mechanical Fastening Adhesive Bonding Thermoset Matrix Composites Mechanical Fastening Adhesive Bonding Hybrid (Mechanical + Adhesive) 4/3/2015 PKM 7

8 Joining Options Between Dissimilar Materials Material Combination Steel and Al Alloys Steel and Mg Alloys Al and Mg Alloys Steel and CFRP Joining Options Arc Welding (Cold Metal Transfer, Transition Inserts), FSW, SPR, Clinching, Adhesive Bonding SPR, Bolting, Adhesive Bonding SPR, Bolting, Adhesive Bonding Adhesive Bonding, Bolting, Hybrid Joining 4/3/2015 PKM 8

9 Friction Stir Spot Welding of Aluminum and Polypropylene (Research at the University of Michigan-Dearborn) Average Failure Loads for all Joint Configurations TOP VIEW Average Failure Load (kn) Highest Average Failure load for Adhesive Joints Lowest Average Failure loads for Adhesive Joints Highest Average Failure load for Friction Joints Lowest Average failure Loads for Friction Joints Adhesive joints Friction joints Type of Joint BOTTOM VIEW 4/3/2015 PKM 9

10 Material Properties Consideration Mechanical Strength (Yield or Tensile) Elastic Modulus Formability (n and r) Thermal Coefficient of Thermal Expansion Thermal Conductivity Melting Temperature Compatibility Metallurgical compatibility (Solubility, Chemical Reactivity, Wettability, etc.) Electrochemical compatibility 4/3/2015 PKM 10

11 Mechanical Properties Material Density (g/cm 3 ) Modulus (GPa) Yield Strength (MPa) Tensile Strength (MPa) DQ Steel % Elongation DP Steel Boron Steel AA AA-6011-T MA-AZ31-H MA-AZ91D CFRP (0/90/45) /3/2015 PKM 11

12 Thermal and Electrical Properties Material Coeff. of Thermal Expansion (10-6 / o C) Thermal Conductivity (W/m. o K) Electrical Resistivity (-cm) Specific Heat (J/g. o K) Melting Range ( o C) Steels Al Alloys Mg Alloys Polymers CFRP /3/2015 PKM 12

13 Corrosion Material Corrosion Potential (V) Iron Environmental Consideration Aluminum Formation of Surface Layer Magnesium Formation of Surface Layer Polymers --- Temperature, Humidity, Auto Fluids CFRP --- Temperature, Humidity, Auto Fluids 4/3/2015 PKM 13

14 Joints of Dissimilar Materials Differences in modulus, yield strength and strain hardening characteristics High stresses at the interface between dissimilar materials Stress concentration at the interface corners and corner cracks Unwanted springback, especially in tailorwelded blanks (due to difference in yield strength to modulus ratio) 4/3/2015 PKM 14

15 Joints of Dissimilar Materials Difference in coefficients of thermal Detrimental residual stresses after the joining operation and/or thermal stresses during the service period Distortion and dimensional problems Microcracks and microvoids 4/3/2015 PKM 15

16 Joining of Dissimilar Materials Joining with composite materials must Are anisotropic Do not show yielding Have different failure modes (debonding, delamination, etc.) May not formable Are not weldable Have different surface characteristics than metals 4/3/2015 PKM 16

17 General Considerations for Joint Development Material combination (Difference in material characteristics) Performance requirements Material thickness Joint design (type, overlap, distance between joints, joint pattern, etc.) Thermal expansion Potential for corrosion and environmental degradation Need for mechanical fixtures and constraints 4/3/2015 PKM 17

18 Considerations for Liquid Phase Welding Pre-joining surface condition and surface treatments Difference in melting temperatures Heating and cooling rate effects on the microstructure Formation of brittle intermetallic compounds during joining Post-joining stress-relief treatments 4/3/2015 PKM 18

19 Evaluation of Joints Strength Durability Degradation Other Lap Shear T-Peel Fatigue Crash Creep Galvanic Corrosion Environmental Degradation Phase Diagram Failure Modes Microstructure Fracture Toughness 4/3/2015 PKM 19

20 Static Test Methods Lap Shear Test T-Peel Test 4/3/2015 PKM 20

21 Fatigue Test Methods Shear Fatigue 4/3/2015 PKM 21

22 Fatigue Test Methods Tension Fatigue 4/3/2015 PKM 22

23 Corrosion Test Methods Base Materials and Joined Materials Laboratory Tests for Basic Corrosion Behavior in Automotive Environment Weight Loss in Immersion Tests, Polarization Tests Effect of Corrosion on Mechanical Properties Accelerated Cyclic Corrosion Tests in Salt Solution Salt Spray Tests In-Vehicle Tests 4/3/2015 PKM 23

24 Adhesive Joining With increasing use of dissimilar materials, adhesive joining is becoming more accepted. Numerous advantages: More uniform stress distribution Increases structural stiffness Little or no alteration of the substrate properties Less dependent on the materials to be joined Relatively easy to adopt on the production line 4/3/2015 PKM 24

25 Considerations for Adhesive Joining Adhesive selection issue Adhesive properties Surface preparation issues Joint design issues Quality control issues (including NDT) Environmental degradation Long term durability Creep, Fatigue 4/3/2015 PKM 25

26 Adhesive Properties Shear modulus, shear strength, shear strain-to-failure Stress-strain properties (needed for FEM) at RT, low and high temperatures Coefficient of thermal expansion Fracture toughness (Resistance to crack propagation determined by DCB test) Creep (long-term) Effect of environment (moisture, elevated temperature, freezing temperatures, salt, etc.) both short term and long term Adhesion properties (e.g., surface energy) Chemical resistance Viscosity 4/3/2015 PKM 26

27 Adhesive Selection Adhesive selection depends on Performance requirements Surfaces to be bonded Adhesive curing or bonding time Expected service environment (temperature, humidity, etc. Adhesive application method Cost 4/3/2015 PKM 27

28 Adhesive Joint Evaluation Static Tests, such as Lap Shear, T- Peel, Wedge Fatigue Tests Dynamic Tests (Impact, Vibration) Creep Tests Environmental Tests (Elevated Temperatures, Freezing Temperatures, Salt Solution, etc.) 4/3/2015 PKM 28

29 Conlusions Joining of dissimilar materials is one of the key challenges in a multi-material automotive structure. Evaluation of dissimilar joints should not only include a variety of short-term and long-term tests, but also analytical tools, such as FEM with realistic material properties. 4/3/2015 PKM 29

30 Thank you. 4/3/2015 PKM 30