Recycling-friendly rolled aluminium products with outstanding surface quality
Sustainable perfection
Approaches to tackling decarbonization by increasing scrap utilization and switching to renewable energy sources influence the entire process chain for producing sheets and plates.
In times when sustainability and environmental protection are growing in importance, industry is turning its attention to green aluminium production. Political frameworks and societal conditions have set clear targets in this regard, with initial concepts to achieve these goals already translated from theory into practice. Sustainable business and production activities are a top priority for AMAG. Sustainability is firmly established in the company’s culture. AMAG’s comprehensive sustainability strategy encompasses environmental, social and economic goals and explicitly includes a clear commitment to continuously reduce the company’s CO2 emissions.
It is essential that AMAG implements and evaluates technical measures in order to achieve these goals. The company has various levers available to pull throughout the process chain, each with different potential to reduce its CO2 emissions. The roadmap for this ongoing adaptation has been defined: in addition to step-by-step implementation planning, it also sets priorities for the necessary implementation concepts. In principle, adjustments and changes to established technical processes have the potential to negatively impact product quality. This is why, given their number and variety, the changes planned in pursuit of carbon neutrality call for a high level of scientific preparation. Scrap selection - i.e. processing and sorting the scrap - is one of the first steps in a product’s journey through the AMAG site. AMAG can draw on decades of experience in successful recycling. This is linked to the company’s ever-growing portfolio of plant and machinery, which includes state-ofthe- art scrap sorting technology. Almost all scrap can be sorted and processed in Ranshofen. An average recycling rate of 75-80% testifies to both the company’s technical capabilities and the economic and environmental importance of scrap processing. In comparison to processes using primary materials, aluminium recycling cuts energy requirements by up to 95%. This is why processing scrap and furthering AMAG’s recycling expertise form a fundamental building block in the company’s decarbonization strategy. In addition to modern sorting systems and processing techniques, further increasing scrap utilization levels in future will ultimately also require a willingness from customers to use these products. Although aluminium is infinitely recyclable in theory, it is not possible to prevent an increase in levels of tramp elements below a certain level. Levels of elements such as iron and copper increase over time, which can influence products’ corrosion behavior. Adjustments are therefore required to the thermomechanical process route to fully safeguard product quality. With this in mind, complete decarbonization will require far more than simply increasing the scrap content of aluminium alloys. AMAG has therefore defined two other areas that could contribute to achieving a decarbonized production site. For one, technical measures should improve energy efficiency, thereby reducing total energy consumption. For another, the deployment of new technologies will facilitate a transition from fossil fuels to renewable energy sources. The most prominent example is switching from natural gas to hydrogen. Testing is currently underway at AMAG’s casting plant. Not only does migrating to other energy sources entail certain technical challenges, it also calls for re-evaluation of potential negative effects on product quality. Hydrogen combustion, for example, involves a different furnace atmosphere. Key issues in this context include how this different atmosphere influences the melt and the subsequent casting process.
However, these considerations also include less energy-intensive processes than smelting. Reduced process temperatures and throughput times also make a noteworthy contribution to cutting CO2 emissions. These process parameters demand particularly detailed analysis to avoid compromising specific product properties and comply with all quality parameters. Initial trials are already underway and, if successful, could be incorporated into series production. All of these changes to the material’s chemical composition and processing inevitably has an impact on its surface characteristics. AMAG has an array of methods at its disposal to inspect product quality, especially the surface quality of its materials. Numerous optical inspection systems (OIS) are positioned throughout the process chain. Even at the high speeds used in cold rolling, these systems can systematically examine surfaces before identifying and classifying defects. While information from this measurement system is used directly in material evaluations, it is also used to inform cutting patterns so that any material with identified defects can be removed from the final systems. In parallel with these high-tech systems, AMAG also relies on the human eye, so employees at visual inspection stations (VIS) scrutinize the coil as it passes. The color and intensity of the lighting system can be adjusted to assist this visual inspection. This method allows fine-tuning in many process steps, such as during the chemical pretreatment spraying process for surfacesensitive automotive materials. AMAG has introduced internal test procedures for certain products, including to assess the surface quality of high-sheen products. An in-house pilot plant for anodizing processes features an immersion tank for pickling and anodizing processes, with material samples tested in line with customers’ requirements. The luster and quality criteria for the resulting oxide layer can be used to monitor material quality and optimize production processes. This rapid and efficient provision of information about AMAG products represents an important strategic measure to ensure surface quality, especially in conjunction with the new continuous coil coating line. This new line performs chemical treatment, including for architectural, soldering and high-gloss materials, in order to remove deformities and impurities from the uppermost material layers. The result is very clean, defect-free surfaces that are highly functional and optimized for subsequent process steps (Figure 1).
However, sensitive surface qualities are heavily influenced by early process steps. Hot strip sections, for example, can be subjected to targeted processing through chemical processes at t Figure 2: The exterior of the Center for Material Innovation he anodizing pilot plant and prepared for further examination. Pickling reactions, for example, can reveal and amplify roughness, making visible any deformations in the surface caused by upstream rolling processes. This makes it possible to implement optimizations and draw conclusions regarding the influence of roller coarseness, reduction per pass and even the emulsion composition. In addition to these surface inspection stations on production lines, AMAG also has a cutting-edge test laboratory. The Center for Material Innovation (Figure 2) is AMAG’s research and testing facility. AMAG has unparalleled expertise, including specialists in chemistry, metallography, microscopy, environmental measurement engineering, materials testing and surface technology. Its laboratories are accredited to the highest Austrian standards. In addition to a series of other certifications, it is also a certified NADCAP Materials Testing Laboratory for aviation products. AMAG conducts testing to determine key product quality characteristics in line with international standards, which enables AMAG to offer its customers material information of the utmost reliability. These standardized tests are primarily used as an approval criterion for AMAG products and are therefore conducted in high volumes (examples of annual measurement volumes: >100,000 tensile tests, >7,000 structure characterization tests, >6,000 corrosion tests, >2,500 passivation layer analyses). Products that are produced and sold - by customer request - under the AL4® ever brand are subject to the same high quality standards and subjected to the same material tests. Given these wide-ranging testing capabilities, AMAG can swiftly and efficiently identify deviations in quality and thus prevent them.
In products for the automotive sector, Ti/ Zr passivation of coil material represents a highly surface-sensitive process. The wetchemical coating process in passivation requires a high degree of precision and continuous monitoring, with typical coating layers applied at 4 mg/m². At AMAG, this very thin layer is exclusively applied using the roll-coater system. Besides achieving a precise coating, this process is also more environmentally friendly than spraying on the coating. In this roll-coater technique, the watery passivation liquid is applied to the coil surface by rollers, which only uses the amount of liquid actually required and also generates no chemical waste. The applied coating is analyzed in the laboratory using modern X-ray fluorescence devices and evaluated for approval. Surface testing for Ti/Zr-passivated automotive coils is, therefore, a particularly important part of the approval process for two reasons: it measures a quality parameter of the material but also allows us to draw conclusions about the stability of chemical production processes. At AMAG, each passivated coil is inspected to ensure consistent and precise application of the Ti/Zr passivation layer (Figure 3).
AMAG conducts tailored material tests and characterization methods for new products, process developments and optimizations throughout the production route. The rapid adhesion test, is one example of a new and innovative test technique that was developed in-house. Determining the adhesion performance of aluminium materials is an exceptionally time-intensive test method for one of the most surface-sensitive quality parameters. This joining technique is increasingly important, especially for bodywork construction in the automotive sector. Adhesion behavior is therefore an important material requirement. Different adhesives are used for different specific applications and by different customers, which in turn calls for different testing and assessment methods. Adhesion testing with structural adhesives is a particularly sophisticated test variant in which the sample is artificially aged for up to 3,000 hours in a neutral salt spray test. The aluminium’s bordering surface with the adhesive is the decisive factor: insufficient surface quality will inevitably cause an adhesive joint to fail. In its rapid test, AMAG has successfully reduced the artificial aging to around 300 hours in by amending the sample production process and the test conditions. Nevertheless, the results of this accelerated aging method is an effective way to conduct high-quality assessments of adhesion performance in series operation. This makes it possible to conduct targeted and efficient testing of surface quality during the development and optimization of products and processes. Continuous testing of ongoing production therefore facilitates prompt feedback regarding process-related variations, thereby safeguarding high surface quality. Intensive development work has enabled AMAG to develop extensive expertise in adhesives. This understanding of functional surfaces and the ability to interpret positive and negative adhesion results represents a significant benefit for many individual customer solutions.
