24th International Colloquium Tribology - January 2024 95 Unveiling Extreme Lightweight Potential by PEO Refinement of Innovative Al Alloys Anutsek Sharma 1 , Jörg Zerrer 1 , Genki Funamoto 2 , Anna Buling 1* 1 ELB - Eloxalwerk Ludwigsburg Helmut Zerrer GmbH, Neckartalstrasse 33, DE-71642 Ludwigsburg - Neckarweihingen, Germany 2 Advanced Composite Corporation, 2259-9 Oobuchi, Fuji, Shizuoka, 417-0801, Japan * Corresponding author: buling@cceranod.de 1. Introduction Required component weight reduction often competes against wear and corrosion issues when it comes to lightweight metals. Aluminum (Al) and its alloys are widely used in different industrial applications, e.g., aerospace, automotive and machinery. Further weight reduction of components can be achieved with additively manufacturing methods of Al-alloys. Promising candidates for highly improved mechanical properties can be the aluminum matrix composites (AMCs), where ceramic particles are reinforced in an aluminum matrix. While powder-based 3D printing techniques are limited to the existing powder material and mostly bear high machinery costs by producing high amount of powder waste, the novel liquid metal printing (LMP) technique, developed by GROB Werke GmbH, enables 3D printing using any existing Al wire material without any material waste accompanied by low machinery costs. Unique mechanical properties like high strength and thermal stability of the AC-Albolon ® (AMC) material from Advanced Composite Corporation enable lightweight materials applications, where high rigidity and shape control are required. Plasma Electrolytic Oxidation (PEO) is known as an environmentally friendly technique leading to highly wear and corrosion resistant surfaces on lightweight metals [1]. To unveil further potentials of novel material groups and increasing their use case range, ULTRACERAMIC ® PEO (refinement was applied to LMP and AMC materials. A comparison to the selective laser melting (SLM) produced AlSi10-alloy is provided as well. PEO refined advanced Al alloys were tested under dry sliding conditions using a pin-on-disc system. The coefficient of friction and the wear rate of refined and blank samples were investigated. Initial studies reported a 1000x decrement in wear volume of PEO protected surfaces in comparison to blank samples, which might lead to an extended range of application of these novel lightweight materials. 2. Material and Methods LMP AlSi12 alloy used in the present work is provided by GROB Werke GmbH. LMP has emerged with higher building rates, reduced costs, a possibility of fast scaling up, reduced thermal distortion and increased degree of freedom. For enhanced mechanical and thermal stability, Advanced Composite Corporation developed AC-Albolon ® which is an aluminum matrix composite (AMC) with aluminum borate incorporated particles produced by liquid forging technology, resulting in highly homogeneous and finely dispersed composites. The wear results from pin on disc tests on LMP and AMC produced samples were then compared with additively produced AlSi10Mg samples from Selective Laser Melting (SLM), which is a widely used additively manufactured technique. The coupons manufactured by LMP and AMC had a diameter of 31 mm and were 6 mm in height. To analyze different surface conditions, one side was left in as-built state while the other side was polished to 2500 grit. The samples were refined by ULTRACERAMIC ® PEO process in a low alkaline electrolyte using stainless steel as counter electrode. Figure 1 shows schematically the process with high potentials by a pulsed source. Figure 1: ULTRACERAMIC ® process curve The previously polished side was used to perform tribological tests eliminate the influence of roughness of th manufacturing process. The tribological tests were performed using pin on disc testing setup with tungsten carbide balls as counter bodies. The present work discusses the tests performed at 5 N normal load in linear reciprocal mode at a maximum speed of 4 cm/ s. Sample terminology that will be used in later sections can be seen in Table 1. Table 1: sample terminology Sample Terminology AMC- PEO refined AMC- PEO LMP- PEO refined LMP- PEO SLM- PEO refined SLM- PEO AMC uncoated AMC LMP uncoated LMP SLM uncoated SLM PEO refined samples and uncoated samples exhibit average roughness (R a ) values ranging from 1.2 µm to 7.5 µm. An 96 24th International Colloquium Tribology - January 2024 Unveiling Extreme Lightweight Potential by PEO Refinement of Innovative Al Alloys overview of varying roughness values on polished side is shown in Figure 2 below. Figure 2: overview of average roughness (R a ) values on polished side 3. Results and discussion Development of the coefficient of friction (µ) for reference and PEO refined samples is shown in Figure 3. It can be seen in Figure 3 (a) that the AMC surface shows stable and constant µ while the AMC - PEO showed the lowest friction in comparison to LMP - PEO and SLM - PEO. In Figure 3 (b), a degrading µ for LMP sample can be seen. This surface suffers from increased wear and material transfer to the ball. However, LMP - PEO sample shows a clear running-in behavior. At the start, µ increases and as the testing continues the friction becomes stable. Figure 3 (c) shows µ over testing distance for SLM samples. SLM sample shows similar trend as LMP sample due to the softness of the material. SLM - PEO sample showed steep rise in friction at the start of testing with a subsequent stabilization. Figure 3: Coefficient of Friction (µ) over testing distance for (a) AMC, (b) LMP and (c) SLM produced surfaces It can be seen from these curves that R a has direct impact on coefficient of friction values. The samples with higher average roughness values showed increasing trends in Figure 3 (a), (b) and (c). Figure 4: surface wear coefficients (K surface ) with respect to corresponding samples Figure 4 shows varying coefficients of surface wear (K surface ) for corresponding samples. It can be clearly seen that refining Al samples with PEO provides greater surface protection against wear. AMC - PEO showes the lowest wear followed by LMP - PEO and SLM - PEO. Reference samples, on the other hand, suffered from harsh wear and extensive material transfer to the counter body. 4. Conclusion It can be concluded that refining Al alloys with ULTRAC- ERAMIC ® leads to enhanced wear protection. With above discussion, it can be learned that a wide variety of Al alloys fabricated using various manufacturing methods can be successfully refined with PEO. Following conclusions can be drawn: • The coefficients of surface wear showed a comprehensive increase in wear resistance of PEO refined samples in comparison to reference or uncoated samples. • Unprotected Al surfaces suffer from extensive tribological wear. • Reduced coefficients of surface wear of approximately 10 -3 can be observed on PEO refined surfaces. • Average roughness values have a direct impact on friction. • The PEO process is completely sustainable without usage of harmful chemicals, leading to enhances material wear and corrosion resistance. 5. Acknowledgement ELB - Eloxalwerk Ludwigsburg Helmut Zerrer GmbH thanks GROB Werke GmbH for providing samples. References [1] M. e. al., „Improving the wear resistance of plasma electrolytic oxidation (PEO) coatings applied on Mg and its alloys under the addition of nanoand microsized additives into the electrolytes: A review „Journal of Magnesium and Alloys“, pp. 1164-1186, 2021. https: / / doi.org/ 10.1016/ j.jma.2020.11.016