Design Considerations When Terminating Aluminum Wire
It may be necessary to replace copper wiring with aluminum in automotive applications to reduce vehicle weight and achieve the aggressive future fuel-economy standards, but design engineers must be mindful of the significant differences between aluminum and copper wire terminations.
Aluminum wiring has been used for many years in several different industries. Utility companies have successfully used aluminum wire for the purposes of electrical transmission in power grids; the aircraft industry has successfully used aluminum wiring in power applications. Now the automotive industry is replacing copper wires with aluminum. The primary reasons for this conversion are to reduce costs and vehicle weight in order to achieve the future fuel economy standards.
In the 1960s, due to increasing costs of copper wires, aluminum was used to wire entire houses. It was not entirely successful and connection failures began to occur, resulting in overheated connections and some house fires. There are various opinions as to why this happened, but the most frequently identified reasons are workmanship, thermal expansion differences, and material creep. Significant advances have been made in aluminum wires and terminations since that time, but the stigma of aluminum wiring remains today, at least for house wiring.
To be sure, aluminum is significantly different from copper, and several precautions need to be taken when using it in electrical wiring applications. Much of the following information was extracted from a USCAR Wire Processing Technology Expo session entitled, “Automotive Aluminum Wire…In Your Future,” which was moderated by Don Price, Ph.D., liaison from Ford Motor Company to EWAP of USCAR, LLC. Also on the panel were Rakesh Patel, chairman of ISO Automotive Electrical Cables Committee and Kurt Seifert of Delphi Packard Electrical/Electronic Architecture.
The fuel economy standards for the year 2025 are a fleet-wide average of 54.5 miles per gallon. The lower weight of aluminum as compared to copper may be required to achieve this goal. It takes only one pound of aluminum to equal the current-carrying capacity of two pounds of copper. Additionally, aluminum offers a lower cost per ampere than copper and provides up to a 48% reduction in mass.
Six specific ways that aluminum is more challenging than copper were identified:
- Lower conductivity – Aluminum has about 60% of the conductivity of copper. Therefore, to carry the same current as copper, larger wire-gauge sizes must be used.
- Reduced break strength/flex – Aluminum is a very ductile material and only has about one third of the mechanical strength as copper. This property must be taken into consideration when replacing copper in electrical wiring applications to assure that the required mechanical strength is achieved in the wire itself as well as the pullout strength of the connection to the terminal.
- Oxides form an insulating layer – Aluminum forms a dense and very hard oxide layer on the wire surface. The contact design and termination process must fracture these oxides to provide an excellent metal-to-metal contact.
- Aluminum has different coefficients of thermal expansion than copper – Termination systems need to take this difference into account. Thermal cycling of a termination can create voids leading to loose connections, which cause high-resistance terminations that get progressively worse over time.
- Galvanic corrosion may occur – This phenomenon could happen when two different metals electrically contact each other and an electrolyte is present. When using aluminum wire and copper contacts in the presence of moisture, care must be taken to inhibit galvanic corrosion. Depending on the application, it may be necessary to seal the termination.
- Stress relaxation and creep can loosen terminations – There is a tendency of aluminum to creep and relax under mechanical load and increased temperature. The result will be higher-resistance terminations that may worsen over time. The termination systems need to be designed to be sufficiently robust to prevent this from occurring.
It may be necessary to replace copper wiring with aluminum in automotive applications to reduce vehicle weight and achieve the aggressive future fuel-economy standards. However, design engineers need to be mindful that there are significant differences between aluminum and copper wire terminations; the above-mentioned challenges must be considered and good design practices adhered to in order to ensure robust and reliable wiring systems.
Bill Garver of APEX Electrical Interconnection Consultants has 47 years experience in the connector industry, primarily in the management and direction of new product development and operational division management. He held the titles of division manager and director of development engineering at AMP. Garver developed new products throughout the full product life cycle – concept through introduction – for numerous industries including consumer, commercial, computer, industrial, communications, and medical.