Extrusion Finishes & Fabrication

Thilanka Hettiarachchi, Savonia University of Applied Sciences, Finland 

The surface quality of aluminum extrusions is a critical factor influencing the effectiveness and visual outcome of downstream finishing processes such as anodizing and powder coating. Surface defects including die lines, pickup, streaking, blistering, and surface roughness variations commonly originate during extrusion and tend to become more pronounced after finishing. These imperfections can lead to poor aesthetics, weak coating adhesion, and increased rejection rates in industrial production. This paper reviews the most frequently observed surface defects and examines their root causes in relation to billet quality, extrusion temperature, ram speed, die condition, lubrication, and cooling practices. It also explores the relationship between extrusion-induced surface characteristics and their behavior during surface finishing, based on observations from industrial settings. Strategies for minimizing defects are presented, with an emphasis on process control, die maintenance, and surface preparation methods, aiming to enhance surface integrity, improve coating performance, and reduce material waste. 

Thilanka Hettiarachchi, Savonia University of Applied Sciences, Finland 

The aluminum anodizing process generates hydrogen as a byproduct, which is typically vented to the atmosphere without recovery. This paper explores the feasibility of utilizing this hydrogen for green methanol production via catalytic synthesis with captured carbon dioxide. By integrating anodizing operations with methanol synthesis systems, the approach enhances resource efficiency and reduces carbon emissions associated with aluminum surface treatment. The study examines hydrogen recovery techniques suitable for anodizing lines, carbon dioxide sourcing from nearby industrial exhaust streams, and potential strategies for system integration within aluminum finishing plants. It also considers opportunities for utilizing waste heat and optimizing energy flows across the combined system. The resulting green methanol can serve as a sustainable energy carrier, low-carbon fuel, or chemical feedstock. This approach supports circular economy principles and offers a practical solution for lowering the environmental impact of anodizing while creating additional value within the aluminum industry. 

Rebecca Robbins, Bonnell Aluminum, USA 

Aluminum sulfate (alum), a byproduct of the anodizing process, is a key coagulant in municipal wastewater treatment. It enhances solids removal by forming aluminum hydroxide flocs that improve sedimentation and filtration, and its strong affinity for phosphate makes it essential for meeting increasingly strict effluent phosphorus limits. Collaboration between manufacturers and municipalities can further increase its value; in one case study, recovered alum from a single anodizing plant saved a municipality nearly $3 million in chemical costs. Emerging research highlights additional benefits, including improved filtration performance, reduced chemical consumption, and positive environmental impacts. Overall, alum remains a versatile, cost‑effective solution for solids removal and nutrient control in modern wastewater treatment systems. 

Justin Girard and Ted McElroy, Bulk Chemicals, Inc., USA 

The use of chrome chromate (in Europe) and chrome phosphate (in the USA and Canada) were the mainstay for conversion coating aluminum extrusions for over half a decade (from about 1950 to 2000), but due to heightened concerns over negative health and ecological effects of hexavalent-chromium, and pressure from government legislation to minimize maximum allowable worker exposure and discharge limits, it has become increasingly difficult to use this dated technology. In response, there have been successful efforts to develop acceptable options such as trivalent chrome, which unlike chrome-free, provides bare corrosion protection. This presentation is intended for those that are still utilizing hexavalent chrome. We will explain the ease of making this transition – which is essential for companies to not only demonstrate ecological sustainability, but also good employee stewardship. Furthermore, upon converting to trivalent chrome, applicators often realize cost savings and experience minimal disruption to their processing line. 

Pinakin Patel, Techevon LLC, USA 

This paper will discuss the phenomenon of weathering of anodized aluminum. Anodized aluminum, particularly on architectural panels, tends to develop an iridescent film after installation on buildings which in some cases is heavy enough to create a perception of failure. The paper will try to show the factors that increase or decrease this phenomenon sometimes referred to as weathering bloom. Factors such as type of pretreatment process, current density, sealing methods and seal quality will be used for the evaluation. The paper will show that there is no physical failure by measuring the coating thickness before and after weathering. Finally, methods to clean the weathering bloom will also be discussed. 

George Oh, Quaker Houghton, USA 

Low-ammonia acid etches can produce matte finishes with good appearance and hideability comparable to standard acid etch. However, differences in the chemistry and operational parameters of the two processes can affect other operational factors including amount of metal removed and sludge production. Comparisons between the two etches on both laboratory and manufacturing scale are presented. 

Malgorzata Halseid, Jan Tore Gundersen, Anders Nordeide, Hydro Aluminium Metal, Norway; Takeshi Saito, Hydro Aluminium Metal, Singapore; and Annica Crispin and Magnus Gustavsson, Hydro Extrusions, Sweden 

This work investigates the influence of elevated Cu, Zn and Fe contents on anodizing behavior in recycled AA6060 and AA6063 alloys, with emphasis on surface pretreatment and its impact on surface appearance. Different anodizing routes are discussed, including conventional alkaline etching prior to anodizing, acidic etching and market‑specific process concepts. It is well known that preferential grain etching (PGE) can occur with alkaline etching, especially with elevated Zn presence in the alloy. The results show that PGE can be suppressed with careful management of bath chemistry, including the presence of specific additives. Particular attention is given to the Japanese JIS H 8602‑based anodizing route with very short etching times, thin anodic layers and transparent organic coatings. Acidic etching produces a more uniform morphology but cannot universally replace alkaline etching. Overall, the study highlights how pretreatment selection and bath chemistry affect surface quality in anodized recycled aluminum. 

Malgorzata Halseid, Jan Tore Gundersen, Helga Steenson and Cristina Espezel, Hydro Aluminium Metal, Norway 

As recycled content increases in 6xxx alloys, confidence in corrosion‑assessment methods becomes critical. This work combines two independent datasets to evaluate how well accelerated tests predict real outdoor behavior. For powder‑coated 6060/6063, extended filiform corrosion tests up to 2000h produced measurable filament growth, yet no filiform corrosion has been observed after two years of marine outdoor exposure, demonstrating poor correlation between accelerated filiform corrosion testing and real‑world performance. For bare 6005 and 6082 alloys, ISO 11846 intergranular corrosion tests showed pronounced attack in recycled variants with higher Cu, Zn and Fe, while outdoor exposure resulted only in minor, localized grain‑boundary corrosion, comparable to primary alloy variants. These findings indicate that accelerated tests are effective for ranking materials but do not reliably predict service behavior. More long‑term outdoor exposure data are needed, and current accelerated test protocols may require adjustment to better reflect real environmental conditions. 

Abdul Mobin Mohhamad and Arif Hussain, Gulf Extrusions LLC, United Arab Emirates 

In the aluminum downstream industry, extrusion is a wrought metal process that can affect critical surface imperfections, which will appear as visual defects during the anodizing process. This is caused by inconsistencies during the extrusion process, such as variations in cooling rate, extrusion speed, quenching conditions, die design, and billet quality, which result in a non-uniform surface macro and microstructure. The anodizing and sealing tests will be performed as per Qualanod specifications (Type II – Sulfuric acid). Anodizing is an electrochemical process that thickens and toughens the naturally occurring protective oxide. Process steps are cleaning, pre-treatment, anodizing, and hot sealing. AA6063 (Al-Mg-Si), Case 1: primary aluminum (with peripheral coarse grain (PCG) vs. without PCG zone); Case 2: secondary aluminum (with peripheral coarse grain (PCG) vs. without PCG zone). 

Ilya Ostrovsky and Birgit Fassbender, Chemetall GmbH, Germany; Andrea Monti, Chemetall Italia, Italy; Ruben Martinez, Raynier Castillo and Iris De Graeve, Vrije University Brussel, Research group of Sustainable Materials Engineering, Belgium 

BASF–Chemetall Surface Technologies is advancing sustainable, energy‑efficient solutions for architectural and industrial aluminum finishing through next‑generation anodizing and thin‑film conversion technologies. A newly developed temperature‑tolerant sulfuric acid anodizing process improves operational robustness without the use of weak organic acids. Studies on AA6060/6063 alloys using SEM‑EDX and corrosion testing confirm enhanced microstructure stability and protection at elevated process temperatures. In parallel, a nickel‑free cold‑sealing system delivers exceptional resistance to highly alkaline environments while operating at low temperatures, ensuring full compatibility with all coloring processes. An innovative acid‑etching formulation developed through electrochemical methods enables effective oxide and alloying element removal while minimizing stainless‑steel attack, reducing sludge formation and drastically lowering ammonia in wastewater. Additionally, the Oxsilan Plus thin‑film conversion coating provides superior paint adhesion and corrosion resistance, particularly on recycled aluminum substrates. Together, these technologies deliver sustainable, high‑performance aluminum finishing solutions with improved efficiency, durability, and environmental benefits. 

Anders Nesse, Hydro Extrusions; Ole Runar Myhr, Hydro Aluminium; Trond Furu, Norsk Hydro, Corporate Technology Office, Norway 

Welding is a key fabrication method for joining aluminum components. A major challenge is heat-affected zone (HAZ) softening which yields significant reduction of the load-bearing capacity of welded AlMgSi extrusions. Accurate prediction and quantification of the impact of welding provide an enhanced insight into the extruded components performance during mechanical loading. This enables an intelligent design approach on both the thermal processes and the product. The study investigates the acuteness of current state-of-the-art computational modeling tools in capturing the transformation of material properties throughout the welding and the following post-weld heat treatment process. Specifically, the article evaluates the ability to quantify the thermal field evolution, the softening of the HAZ, and the strength recovery through post-weld heat treatment (PWHT). Designated experiments have been conducted to validate the simulation results. 

Andrea Trevisan, S.A.T. (Surface Aluminium Technologies) s.r.l., Italy 

Aluminum extrusion powder coating is becoming more common in North America. The installation of an industrial coating line requires experienced and skilled man-labor to perform it, plus expensive lifting equipment rental, making the line erection and start-up process a relevant portion of the overall capital investment. This paper presents a solution that drastically reduces the installation and start-up time and describes how a quicker production ramp-up allows an accelerated payback and makes the overall investment more affordable. 

Jude Runge, CompCote International, Inc.; Jacqueline Cook, Reliant Aluminum Products, LLC; Medha Veligatla and Shiqi Zheng, Eurofins EAG Laboratories; and Justin Kessler, Bearcat Anodizing, USA 

Electrolytic coloring is a well-established process, typically produced by architectural anodizers, by which the anodized load is immersed in a metal salt solution and electricity is applied to color the anodic oxide. For the most commonly used metal salt, tin, color can range from a light champagne to a deep black on 6xxx-series alloys. Variation in color and intensity may occur across welded multi-component assemblies, for which the alloy, extrusion, and/or weld quality may vary. Utilizing ultra-microscopy methods of Focused Ion Beam (FIB) and Transmission Electron Microscopy (TEM), a comprehensive investigation is presented that shows the impact of each variable in terms of the polarization effects of the resultant base metal and anodic oxide microstructures on the appearance of the electrolytically colored oxide finish. Corresponding variations in microstructural results obtained via metallography, Scanning Electron Microscopy (SEM) and reflectance are provided that connect common analysis techniques to the ultra-microscopy results. 

Alberto Abad, Alvarez-Schaer, SLU, Spain 

The aluminum recycling process requires only about 5% of the energy needed to produce primary aluminum. For this reason, the use of recycled aluminum is increasingly being specified by architects in green buildings projects. However, even when advanced scrap-sorting technologies are employed, the concentration of alloying elements such as Cu, Zn, and Fe is significantly higher than in primary aluminum. These elements exhibit cathodic behavior with respect to the aluminum matrix, thereby increasing its susceptibility to corrosion. This paper presents the investigation carried out on the influence of these alloying elements on the corrosion resistance of coated aluminum using various characterization techniques, including electron microscopy, and anodic cyclic polarization, as well as corrosion testing. Finally, we show how the selection of an appropriate pre-treatment process, combined with a new chromium-free chemical conversion process, can effectively minimize the influence of these alloying elements on corrosion susceptibility of coated recycled aluminum. 

Martin Koeb, Precision Saws, USA; and Christian Bischofberger, Briganto, Austria 

The Briganto Cross Cut is a universal high-speed precision saw engineered for aluminum extrusion fabrication. This paper presents the system's modular architecture supporting customizable configurations including automatic de-stacking and stacking, side-loading magazines, belt conveyors, and buffering stations for fully automatic plant integration. A clamping and positioning mechanism with top and bottom clamping bars across the full cutting width delivers machine positioning accuracy of ±0.01 inch. A 38-kilowatt saw motor accommodates profiles and solid material up to 10 inches in height and 25.59 inches in width, with automatically adjustable saw stroke. A touchscreen interface with recipe-based control allows operators to input piece size, quantity, and alloy type — automatically optimizing cutting speed, blade projection, rotational speed, and clamping pressure, reducing setup time and operator error. Production data demonstrating throughput gains and dimensional consistency will be presented, illustrating the practical impact of advanced cross-cut technology on modern extrusion fabrication.  

Walter Dalla Barba, Italtecno Solutions, Italy 

Artificial intelligence (AI) and full automation, including the automatic racking and unracking of extruded profiles, are now a reality capable of giving a strong boost to the further development of the anodized aluminum market, and therefore to greater demand from architects and building contractors for anodized aluminum profiles and sheets. This increased demand becomes understandable if we consider that, with new automatic racking and unracking systems and the introduction of AI to improve plant productivity and quality, it will be possible to reduce production costs. Greater demand will also reach the market because architects and builders will have access to finished anodized products with attractive new colors and decorations. These decorations are made possible by a new electrochemical technology which, when applied to sheets prior to the traditional cycle—from degreasing to sealing—creates visible special final effects of high design and guaranteed quality, in compliance with international standards.