6xxx aluminium alloys for high-performance busbars

The global transition toward renewable energy and electrified infrastructure is driving rapid growth in high-power electrical systems. Wind and solar power plants, energy storage systems, electric vehicles, charging infrastructure, data centres and modern power grids all depend on efficient, reliable, and scalable solutions for electrical power transmission and distribution. Within this context, busbars play a critical role as compact conductors designed to carry high currents with low electrical losses and high operational stability.Material selection for busbars has therefore become a strategic factor in enabling cost-effective, lightweight, and sustainable electrification. Aluminium has emerged as a key conductor material in this transition. It is abundant, highly recyclable, and requires only a fraction of the energy for recycling compared to primary production. These attributes align well with decarbonization targets and increasing supply-chain sustainability requirements in large-scale energy systems, [1-3].Busbars are widely used across renewable energy and electrification applications. Typical use cases include DC and AC busbars in solar and wind power inverters, battery energy storage systems, electric vehicle power distribution units, fast-charging stations, industrial power electronics, data centers and modern substations.

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Figure 1: Schematic representation of busbar utilization (orange) in a battery electric vehicle

Comparison with copper

Copper has traditionally been the preferred conductor material in electrical applications due to its high electrical conductivity and long-established use. However, aluminium has already replaced copper in several applications during the 20th century, most notably in high-power transmission lines [2]. This transition has been driven by both technical and economic considerations.Table 1 compares key physical properties of aluminium and copper relevant for electrical applications.

Property Unit Aluminium Copper
Electrical conductivity [MS/m] 35 58
Density [kg/m³] 2.700 8.900
Thermal conductivity [W/m·K] 236 401
Table 1: Comparison of relevant properties between aluminium and copper

Due to its lower electrical conductivity, aluminium typically requires a cross section approximately 1.5 – 1.7 times larger than copper to achieve the same current-carrying capacity. However, given that the density of copper is more than three times higher, this still results in a weight reduction of approximately 48 – 54 % when aluminium is used. This represents a decisive advantage in weight-sensitive applications such as wind turbines, overhead transmission lines, and electric vehicles. A major economic driver for substituting copper with aluminium is the significant and sustained price difference between the two materials. Figure 2a shows the price development of copper and aluminium at the London Metal Exchange (LME) from 1990 to 2026, while Figure 2b illustrates the resulting relative price factor [4].Since around 2004, copper prices have increased disproportionately, resulting in an average price factor of approximately 3.8 relative to aluminium in 2025. When the achievable weight reduction is considered, the effective cost advantage of aluminium increases to a factor of approximately 7.0 – 7.9. For heavy-duty busbars with large cross sections, this represents a substantial cost-reduction potential.

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Figure 2: LME price development of copper and aluminium and resulting, relative price factor [4].

The 6xxx series aluminium alloys

The 6xxx series aluminium alloys, primarily alloyed with magnesium and silicon, are used across a wide range of industries including automotive, aerospace, construction, marine, and consumer applications. Their versatility is based on a combination of good corrosion resistance, moderate to high strength, and excellent formability. In addition, 6xxx alloys are heat treatable, allowing their properties to be tailored through controlled heat treatments for specific application requirements.For electrical applications such as high-performance busbars, 6xxx alloys offer a particularly attractive balance of high electrical conductivity, sufficient mechanical strength, and good formability. Electrical conductivity in these alloys is influenced by three main factors: chemical composition, microstructure, and heat treatment state.

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Figure 3: Impact of selected alloying elements on the ultimate tensile strength (ΔUTS) and electrical conductivity (Δσ)
  • Chemical composition: Alloying elements other than aluminium reduce electrical conductivity by acting as lattice imperfections that scatter conduction electrons. The magnitude of this effect depends on both the type and the location of the alloying element. Elements in solid solution generally have a stronger detrimental effect than those bound in precipitates [1].

Figure 3 illustrates the influence of selected alloying elements (0.01 wt.% in solid solution) on both ultimate tensile strength (ΔUTS) and electrical conductivity (Δσ) [5,6]. Elements such as Mn, Ti, V, and Cr exhibit a particularly strong negative effect on the electrical conductivity.

 

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Figure 4: Impact of microstructural features on ultimate tensile strength (ΔUTS) and electrical resistivity (Δρ), adapted from [1]
  • Microstructural effects: In addition to chemical composition, microstructural features such as grain boundaries and dislocations also scatter electrons and reduce conductivity. Figure 4 shows the calculated influence of grain boundaries, dislocations, solute atoms, and precipitates on both strength and electrical resistivity in a 6xxx alloy [1].
  • Heat treatment and temper:Heat treatment has a decisive influence on the distribution of alloying elements between solid solution and precipitates. Starting from a supersaturated solid solution (SSSS), typically designated as temper T4, artificial aging promotes diffusion and precipitation. For 6xxx alloys, the precipitation sequence is as follows [7,8]:SSSS → clusters → Mg-Si co-clusters → GPI zones → β" (GPII) → β" → β (Mg₂Si)

Peak strength is achieved in the β" stage (T6 temper). At this point, conductivity is improved compared to T4 but still limited by remaining solutes. Continued aging leads to coarser, incoherent precipitates, reducing strength but further increasing conductivity. This overaged condition is designated as temper T7 [9].

Alloys EN AW-6101 and EN AW-6101B

Within the 6xxx series, alloys EN AW-6101 and EN AW-6101B are particularly suitable for busbar applications. Their alloying ranges are shown in Table 2 [10].Both alloys combine moderate Si and Mg contents with tightly controlled impurity levels. This enables excellent electrical conductivity while retaining sufficient precipitation hardening potential for adequate strength. EN AW-6101 typically achieves the highest conductivity due to stricter limits on Mn, which has a pronounced negative effect on conductivity [5]. Both alloys are part of the AMAG product portfolio in various tempers, enabling targeted material selection for specific customer requirements.

Alloy   Si Fe Cu Mn Mg Cr Zn Al
6101 Min. Max. 0.30 0.70 - 0.50 - 0.10 - 0.03 0.35 0.80 - 0.03 - 0.10 Balance
6101B Min. Max. 0.50 0.60 0.10 0.30 - 0.05 - 0.05 - 0.60 - - - - Balance
Table 2: Alloying ranges for EN AW-6101 and EN AW-6101 [wt.%]

Material properties for the different tempers

EN AW-6101 and EN AW-6101B are available in the following tempers:

  • Temper T6: Peak-aged condition - high strength, good conductivity
  • Temper T63: Intermediate condition - good strength, excellent conductivity
  • Temper T7: Overaged condition - moderate strength, excellent conductivity

Figure 5 schematically illustrates the heat treatment cycle and the evolution of strength and electrical conductivity. It can be observed that mechanical strength increases rapidly during the early stages of aging and reaches its maximum in the T6 condition. At this stage, precipitation and the associated depletion of alloying elements from the aluminium matrix are not yet fully completed, resulting in only moderate electrical conductivity. At the opposite end of the aging spectrum, the T7 temper represents a fully overaged condition in which precipitation is largely completed. While this leads to a reduction in strength compared to T6, electrical conductivity is significantly increased. The T63 temper, a designation commonly used by OEMs in the busbar industry, represents an intermediate aging condition between T6 and T7. It offers a balanced combination of good mechanical strength and, due to the asymptotical development indicated in Figure 5, high electrical conductivity, making it particularly attractive for demanding busbar applications.

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Figure 5: Schematic heat treatment schedule and impact of aging conditions on strength and conductivity

Table 3 summarizes the corresponding ultimate tensile strength and electrical conductivity values, with conductivity additionally expressed in %IACS (International Annealed Copper Standard). Due to its lower Mn content, EN AW-6101 can reach a conductivity in excess of 57 %IACS (≥ 33 MS/m). Formability is another key requirement for busbars. Bending tests according to ASTM E290 demonstrate that all listed tempers achieve a bending angle of 90° at a bending factor of 1.

Temper UTS [MPa] Conductivity [MS/m] Conductivity [%IACS]
T6 ≥ 220 ≥ 30 ≥ 52
T63 ≥ 190 ≥ 32 ≥ 55
T7 ≥ 170 ≥ 32 ≥ 55
Table 3: Minimum properties of EN AW-6101 and EN AW-6101B

AMAG portfolio for high-performance busbars

To meet the current-carrying requirements of high-performance busbar applications, sufficient cross-sectional areas are essential. AMAG currently supplies EN AW-6101 and EN AW-6101B in tempers T6, T7, and T63 with thicknesses up to 6.0 mm. Trials for thicknesses up to 8.0 mm are in preparation.Maximum coil widths of up to 1,580 mm provide high design flexibility for busbar manufacturers. In parallel, optimized thermomechanical processing routes are under development, offering further potential improvements in both strength and electrical conductivity.Compared with extrusion-based production routes, rolled busbars provide several inherent advantages. These include tighter dimensional tolerances, improved heat dissipation resulting from an increased surface-to-volume ratio, and a typically higher degree of microstructural homogeneity throughout the product cross section.

Conclusion

The 6xxx series aluminium alloys represent a highly attractive alternative to copper for high-performance busbar applications. Their combination of high electrical conductivity, adequate mechanical strength, excellent formability, and significant cost and weight advantages makes them particularly well suited for modern electrification and renewable energy systems.With its EN AW-6101 and EN AW-6101B product portfolio, AMAG positions itself as a reliable supplier of high-performance aluminium solutions that enable efficient, sustainable, and economically competitive electrical infrastructure in transportation, energy generation, and energy storage applications.

Key customer benefits of AMAG 6xxx series alloys for busbars compared to copper

  • Lower cost (factor 7.0 - 7.9) due to significantly lower material price and reduced weight per ampere
  • Up to 50 % weight reduction, enabling easier handling and lower system loads
  • Improved sustainability, with high recyclability and low CO₂ footprint
  • High design flexibility from excellent formability and broad dimensional portfolio
  • High electrical performance of state-of-the-art 6xxx-series alloys
  • Reliable supply and scalability based on global aluminium availability

References:

[1]   Khangoli S., Javidani M., Maltais A., Chen X. (2022) Review on recent progress in Al-Mg-Si 6xxx conductor alloys. Journal of Materials Research 37:670-691, doi:10.1557/s43578-022-00488-3[2]   Czerwinski F. (2024) Aluminium alloys for electrical engineering: a review. Journal of Materials Science 59:14847-14892, https://doi.org/10.1007/s10853-024-09890-0[3]  Sampaio R., Zwicker M., Pragana J., Bragança I. et al. (2022). Busbars for e-mobility: State-of-the-Art Review and a New Joining by Forming Technology. In Davim JP (Ed.), Mechanical and Industrial Engineering. Materials Forming, Machining and Tribology. Springer, Cham, p 111-141, https://doi.org/10.1007/978-3-030-90487-6_4[4]   London Metal Exchange (2026). In: LME Historical Market Data - LME Monthly Average Prices. https://www.lme.com/en/Market-data/Accessing-market-data/Historical-data. Accessed 15 January 2026[5]   Bunte C., Glassel M., Medina C., Zaclman D. (2015) Proposed Solution of Random Characteristics of Aluminium Alloy Wire Rods Due to the Natural Aging. Procedia Materials Science 9:97-104, https://doi.org/10.1016/j.mspro.2015.04.012[6]   Fortin P. (1972) Factors influencing electrical conductivity and strength of aluminum and its alloys. Canadian Metallurgical Quarterly 11(2):309-315, https://doi.org/10.1179/cmq.1972.11.2.309[7]   Banhart J., Sin Ting Chang C., Liang Z. et al. (2010) Natural Aging in Al-Mg-Si Alloys - A process of unexpected complexity. Advanced Engineering Materials 12(7):559-571, https://doi.org/10.1002/adem.201000041[8]  Aruga Y., Kozuka M., Takaki Y., Sato T. (2016) Effects of natural aging after pre-aging on clustering and bake-hardening behaviour in an Al-Mg-Si alloy. Scripta Materialia 116:82-86, https://doi.org/10.1016/j.scriptamat.2016.01.019(Ed.), Light Metals 2024, Springer Nature Switzerland, Cham, 2024, pp. 226-233.[9]  Lin G., Zhang Z., Wang H., Zhou K., Wei Y. (2016) Enhanced strength and electrical conductivity of Al-Mg- Si alloy by thermo-mechanical treatment. Materials Science and Engineering:A 650:210-2017, https://doi.org/10.1016/j.msea.2015.10.050[10]  European Committee for Standardization. (2024). EN 573-3:2024-08-01 Aluminium and aluminium alloys — Chemical composition and form of wrought products — Part 3: Chemical composition and form of products

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