Improving Electrical Conductivity of Commercially Pure Aluminium: The Synergistic Effect of AlB8 Master Alloy and Heat Treatment

This paper summary is based on the article "Improving Electrical Conductivity of Commercially Pure Aluminium: The Synergistic Effect of AlB8 Master Alloy and Heat Treatment" presented at the "MDPI Materials"

1. Overview:

Title: Improving Electrical Conductivity of Commercially Pure Aluminium: The Synergistic Effect of AlB8 Master Alloy and Heat Treatment
Authors: Yusuf Zeybek, Cemile Kayış, and Ege Anıl Diler
Publication Year: 2025
Publishing Journal: Materials (MDPI)
Keywords: commercially pure aluminium, electrical conductivity, aluminium-boron master alloy, grain-coarsening heat treatment, efficiency of electrical motor

Figure 1. Diagram illustrating the production stages of squirrel cage rotors, heat treatment application, and subsequent manufacturing stages of induction electric motors.
Figure 1. Diagram illustrating the production stages of squirrel cage rotors, heat treatment application, and subsequent manufacturing stages of induction electric motors.

2. Research Background:

In the context of escalating global energy demands and the imperative to mitigate greenhouse gas emissions, enhancing energy efficiency has become a paramount concern. Electric motors, extensively utilized across industrial and commercial sectors, present a significant opportunity for efficiency improvements. Commercially pure aluminium (CP-Al) is frequently employed in the fabrication of squirrel cage rotors for induction motors owing to its advantageous low density and cost-effectiveness. However, the inherent electrical conductivity of aluminium, while substantial, can be further optimized to enhance motor performance.

Existing methodologies for improving the electrical conductivity of aluminium often involve the utilization of rare earth elements. While effective, these approaches are associated with considerable cost implications. Aluminium-boron (Al-B) master alloys offer a more economical alternative for impurity reduction in aluminium. Nevertheless, the application of Al-B master alloys can induce grain refinement, potentially counteracting the desired enhancement in electrical conductivity due to increased grain boundary scattering. Therefore, a critical need exists for a cost-effective strategy that not only leverages the impurity removal capabilities of Al-B master alloys but also mitigates the grain refining effect to maximize the electrical conductivity of CP-Al for electric motor applications.

3. Research Purpose and Research Questions:

This research endeavors to significantly improve the electrical conductivity of commercially pure aluminium. The primary objective is to minimize both impurities and grain boundaries within the aluminium microstructure, thereby enhancing the efficiency of electric motors utilizing squirrel cage rotors made from this material.

The key research questions addressed in this study are:

  • How does the incorporation of an AlB8 master alloy influence the purity level and electrical conductivity of commercially pure aluminium?
  • What is the effect of a grain-coarsening heat treatment on the grain size and electrical conductivity of commercially pure aluminium?
  • Does a synergistic effect exist between the addition of AlB8 master alloy and grain-coarsening heat treatment in enhancing the electrical conductivity of commercially pure aluminium?
  • To what extent does the improvement in electrical conductivity translate to enhanced efficiency in electric motors?

The central research hypothesis posits that the combined application of AlB8 master alloy addition and a subsequent grain-coarsening heat treatment will synergistically and significantly elevate the electrical conductivity of commercially pure aluminium, ultimately leading to a measurable improvement in the efficiency of electric motors.

4. Research Methodology

This study employed a rigorous research methodology based on statistical experimental design and response surface methodology, utilizing the Box–Behnken design.

  • Research Design: A Box–Behnken experimental design was implemented to investigate the effects of three factors: boron addition level, heat treatment temperature, and holding time, on the electrical conductivity of commercially pure aluminium.
  • Data Collection Method: Electrical conductivity measurements were performed using a SIGMASCOPE® SMP10 instrument, employing the eddy current method as per DIN EN 2004–1 and ASTM E1004-17 standards. Microstructural characterization was conducted via optical microscopy, with grain size analysis performed using ImageJ software. Motor performance evaluations were carried out using KISTLER motor testing equipment. Chemical composition analysis was achieved through optical emission spectrometry.
  • Analysis Method: Analysis of Variance (ANOVA) and regression analysis, facilitated by Design Expert Version 13 software, were utilized to assess the statistical significance of the factors and their interactions on electrical conductivity. Response surface plots and contour plots were generated to visualize the relationships between variables and the response.
  • Research Subjects and Scope: The study focused on commercially pure aluminium with a purity of 99.7%. An AlB8 master alloy was introduced to achieve boron additions of 0.05 wt.% and 0.1 wt.%. Squirrel cage rotors were manufactured using high-pressure die-casting. Grain-coarsening heat treatments were conducted at temperatures of 450 °C, 500 °C, and 550 °C, with holding times of 2 h, 6 h, and 10 h.

5. Main Research Results:

The experimental results demonstrated a significant enhancement in the electrical conductivity of commercially pure aluminium through the synergistic application of AlB8 master alloy addition and grain-coarsening heat treatment.

  • Key Research Results: The most significant improvement in electrical conductivity was achieved with a combination of 0.05 wt.% boron addition and a grain-coarsening heat treatment at 550 °C for 10 h. This hybrid approach increased the electrical conductivity from an initial 60.62% IACS to 63.1% IACS. Correspondingly, the efficiency of electric motors fabricated with rotors produced using this method increased from 90.35% to 91.53%. Spectral analysis confirmed that boron addition effectively reduced impurities, particularly transition metals like Titanium (Ti), Vanadium (V), and Zirconium (Zr). Microstructural analysis revealed that heat treatment effectively promoted grain coarsening, reducing grain boundary density.
  • Statistical/Qualitative Analysis Results: ANOVA indicated that boron addition, heat treatment temperature, holding time, and their quadratic and interaction effects (excluding the interaction between boron addition and holding time) significantly influenced electrical conductivity (p < 0.05). The regression model exhibited a high coefficient of determination (R² = 0.9859), indicating a strong model fit.
  • Data Interpretation: The enhanced electrical conductivity is attributed to the combined effects of impurity removal by boron addition and the reduction of grain boundary scattering through grain coarsening heat treatment. The synergistic effect underscores the importance of optimizing both material purity and microstructure for achieving superior electrical performance.

Figure Name List:

  • Figure 1. Diagram illustrating the production stages of squirrel cage rotors, heat treatment application, and subsequent manufacturing stages of induction electric motors.
  • Figure 2. Schematic illustration of impurity removal through boron addition.
  • Figure 3. Squirrel cage rotor and its components manufactured from commercially pure aluminium via the high-pressure casting method.
  • Figure 4. Assembly of induction motor with a squirrel cage rotor.
  • Figure 5. Electrical conductivity measurement for the aluminium specimens.
  • Figure 6. Performance testing of induction motors.
  • Figure 7. Box-Behnken design cube with the centre point (0,0,0) and twelve factorial points of three factors, each at three levels.
  • Figure 8. Optical micrographs of the non-treated and heat-treated aluminium specimens.
  • Figure 9. Grain size analysis of the non-heat-treated aluminium specimens.
  • Figure 10. Grain size analysis of the heat-treated Al-0.05B specimens.
  • Figure 11. Contributions of linear, quadratic, and interaction terms affecting electrical conductivity.
  • Figure 12. Correlation graph between the predicted and experimental values of electrical conductivity.
  • Figure 13. Main effect plots of boron addition, heat treatment temperature, and holding time on electrical conductivity.
  • Figure 14. Two-dimensional contour plot and 3D response surface plot showing the effect of interactions on electrical conductivity.
  • Figure 15. Relation between the motor efficiency and electrical conductivity of non-treated and heat-treated aluminium specimens.
Figure 2. Schematic illustration of impurity removal through boron addition.
Figure 2. Schematic illustration of impurity removal through boron addition.
Figure 3. Squirrel cage rotor and its components manufactured from commercially pure aluminium via the high-pressure casting method.
Figure 3. Squirrel cage rotor and its components manufactured from commercially pure aluminium via the high-pressure casting method.
Figure 4. Assembly of induction motor with a squirrel cage rotor.
Figure 4. Assembly of induction motor with a squirrel cage rotor.
Figure 6. Performance testing of induction motors.
Figure 6. Performance testing of induction motors.

6. Conclusion and Discussion:

  • Summary of Main Results: This study successfully demonstrated that a hybrid approach combining AlB8 master alloy addition and grain-coarsening heat treatment is an effective method for enhancing the electrical conductivity of commercially pure aluminium, leading to a notable improvement in electric motor efficiency.
  • Academic Significance of the Research: The research contributes to the fundamental understanding of synergistic material processing techniques for optimizing metal conductivity. It highlights the interplay between impurity control and microstructure engineering in achieving enhanced electrical properties.
  • Practical Implications: The findings offer a viable and cost-effective methodology for improving the performance of electric motors utilizing commercially pure aluminium. This approach has significant practical implications for enhancing energy efficiency in various industrial applications and promoting sustainable manufacturing practices.
  • Limitations of the Research: While the study effectively addressed electrical conductivity enhancement, it did not primarily focus on the mechanical properties of the modified aluminium. The applicability of pure aluminium, even with enhanced conductivity, may be limited in scenarios demanding high mechanical strength.

7. Future Follow-up Research:

  • Directions for Follow-up Research: Future research should focus on further enhancing the mechanical properties of commercially pure aluminium while maintaining or improving the achieved electrical conductivity. This could involve exploring different alloying additions or alternative heat treatment regimes.
  • Areas Requiring Further Exploration: Further investigation is warranted to assess the impact of this hybrid approach on other critical material properties, such as thermal conductivity and corrosion resistance. Exploring the broader industrial applications of this enhanced commercially pure aluminium in diverse sectors, including automotive and energy, is also recommended.

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9. Copyright:

This material is Yusuf Zeybek, Cemile Kayış, and Ege Anıl Diler's paper: Based on "Improving Electrical Conductivity of Commercially Pure Aluminium: The Synergistic Effect of AlB8 Master Alloy and Heat Treatment".
Paper Source: https://doi.org/10.3390/ma18020364

This material was summarized based on the above paper, and unauthorized use for commercial purposes is prohibited.

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