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Maintaining material quality on the road to light-weighting

The big driver behind automotive evolution is the environment. Current legislation aimed at reducing emissions is propelling innovation in the materials used for car components and, as global standards get more stringent, the pace of change is quickening.

Tough legislation on carbon emissions and fierce competition are causing rapid changes across the automotive supply chain. As CO2 emissions fall by 8.5g per 100km for each 100kg lost, cutting vehicle weight remains high on the agenda. Manufacturers are striving to get more out of every drop of fuel and, for EVs (electric vehicles), from a single charge.

 

Ultimately, the answer is to reduce weight by using lighter components across the entire vehicle, no matter which powertrain technology you are working with, and replacing steel with lighter materials makes the most difference. However, the road towards light-weighting brings crucial materials analysis and quality control challenges.

 

There are four key technologies for materials analysis: laser induced breakdown spectroscopy (LIBS), optical emission spectroscopy (OES), thermal analysis (TA) and X-ray fluorescence (XRF). OES, XRF and LIBS are all quite versatile, particularly when it comes to identifying metals. TA on the other hand studies the properties of materials as they change temperature.

 

Here we consider how the technologies are enabling the industry to ensure materials meet quality requirements.

 

The driving force behind change

The big driver behind automotive evolution is the environment. Current legislation aimed at reducing emissions is propelling innovation in the materials used for car components and, as global standards get more stringent, the pace of change is quickening.

 

To combat increased pollution, the European emissions standards have become more challenging. Under the current regulation, Euro 6, we’re about to enter the next phase of standards, where average CO2 emissions of new cars must be a maximum of 95g/km by 2021. Moreover, the EU set CO2 emissions reduction targets of 15% by 2025 and 37.5% by 2030. This has resulted in most manufacturers developing electric powertrain technology and striving to reduce weight.

 

The World Harmonised Light Vehicle Testing Procedure (WLTP) came into effect in 2018 to make sure that new cars are meeting the Euro 6 standard; and is designed to reflect real driving conditions when assessing CO2 emissions.

 

In China, standards have also been getting more stringent. China 6a, compliant with European emission standards, is set to come into force in 2020, with a further standard due in 2023. The standards will be verified under the WLTP and the target is to reduce CO2 emissions by over 90%. Similarly, with 75% of carbon monoxide pollution in the USA attributed to motor vehicles, the Environmental Protection Agency announced in January 2020 that it’s working on new rules to decrease vehicle emissions and cars are set to get lighter, following the global example.

 

The automotive industry and its supply chain, therefore, need to work collaboratively to deliver materials innovations to the industry to make cars lighter.

 

The rise of lighter-weight metals

The automotive industry has very exacting requirements for components. Safety is obviously a priority and many components must be ductile to absorb energy on impact, while other parts must have strength to maintain structural rigidity.

 

The development of new alloys is a very exact science and analysing the melt chemistry down to the ppm level is crucial to avoid residual elements, which can impact on the properties of the alloy. Aluminium and magnesium alloys have won favour in the industry because they are light, relatively low cost and give many of the properties needed. They can be formed into complex shapes including engine components, gearbox housings and structural parts. In fact, the global market for these parts is predicted to grow at a CAGR of almost 7% to a market size of $48 billion by 2021.

 

Aluminium

Weighting one third compared to typical steel, aluminium’s use in cars has sky-rocketed in recent years. In 2018, BMW won an award for a concept to reduce the weight of the tailgate in its 5 Series model. By using aluminium in place of deep-drawn steel sheets, BMW reduced the tailgate from 24.6kg to 11.6kg. By 2022 the average car is expected to contain almost 100kg of aluminium as a replacement of heavier parts. The automotive industry will make up a quarter of all aluminium consumption (30 million tonnes) by 2025.

 

However, to substantially increase the strength of aluminium, you need to add lithium. The third generation of Al–Li alloys could become integral to various components of luxury cars, combining low density, strength, stiffness and damage tolerance.

 

As aluminium is enhanced, technologies are developing to provide effective materials analysis. The preferred choice for fast aluminium alloy sorting is a handheld LIBS analyser, whilst OES instruments can analyse very low levels of lithium in aluminium, down to 0.0005%, in addition to phosphorus and sulphur. Phosphorous and sulphur are normally added to improve machineability; however, they both have a detrimental effect on corrosion resistance so need to be added in small amounts.

An analyser that is optimised for analysing aluminium alloys will enable manufacturers to be more effective with materials analysis. Ideally it should feature a high-performance spectrometer that enables the measurement of lithium in aluminium alloys and is capable of measuring boron-aluminium alloys. Boron and lithium cannot be measured with any handheld XRF analyser. If you need concentrations of boron lower than 5ppm, then you should choose an OES analyser for the best results.

 

Magnesium

Magnesium is lighter than aluminium and has the highest strength to weight ratio of all structural metals. It’s abundant and easily recyclable, so it’s not surprising that it has replaced steel and aluminium in housings and space frames and been used extensively in alloys with aluminium. Opel has used magnesium for dashboard support in the Vectra model, saving 5kg compared with the steel tube previously used, and simplifying the manufacturing process.

 

Magnesium does have drawbacks; it’s brittle and doesn’t have the creep resistance of aluminium. However, innovations could see that problem resolved. A team at Monash University in Australia has created a process to change the microstructure of magnesium so it can be compressed to any shape at room temperature without cracking. The USA Department of Energy has also developed a process that improves the energy absorption and ductility of magnesium, making it more feasible for a larger range of car parts.

 

The quality of new alloys being developed stems from manufacturers having the right tools. From making sure the right material is used to controlling the metal melt, it is crucial for organisations to invest in an analyser that provides results fast and accurately for decision making. For analysis of alloys to the ppm level, OES technology gives the most precise results, as the technology covers the complete spectrum of elements in metal, including phosphorous, sulphur and boron, which can’t be measured at all or with the necessary detection limits with either a handheld LIBS or XRF analyser. The new generation of OES analysers are designed for fast, reliable and cost-effective melt and raw material analysis. They allow analysis of all main alloying elements and identification of exceptionally low levels of tramp, trace and treatment elements in metals.

 

Steel poised to make a comeback

many steelmakers are developing a super-lightweight steel that is stronger, cheaper and almost as lightweight as aluminium in a bid to regain market share. It’s going to be hard to resist the allure of greater strength and lower cost, and with new products expected on the market in 2021.

 

In five years, it’s likely that vehicles will use a larger range of materials than ever before. Therefore, the need to use the right material for the right component and verification of material grade composition will be paramount.

 

Many foundries already use an analyser at the time of dispatch. Inspection when raw materials arrive and then again on the factory floor is equally valuable. It is becoming increasingly important to ensure teams have tools such as handheld XRF and LIBS or OES on hand for materials analysis and quality checking to verify material grades.

 

Composites as an alternative

30% lighter than aluminium and 25% the weight of steel, using composites is another route to reduce weight and improve fuel economy in cars. Their durability and ability to be moulded into variety of complex shapes without the need for high-pressure tools brings improved production efficiency and reduced costs.

 

Virtually all TA techniques can be used for quality control, and research and development within the automotive industry. Typically, DCS analysers are used for glass transition, crystallisation behaviour, reaction enthalpies and kinetics, and the influence of fillers; TMA analysers study the expansion or shrinkage of materials; and DMA analysers are best used for characterizing the frequency, force and amplitude-dependent mechanical behaviour of materials.

 

Conclusion

The field of materials analysis has been rapidly changing in recent years to keep pace with new regulations and innovations in the industry. The continued development and application of technologies like OES, XRF, LIBS and TA is making analysis easier for companies across the automotive industry, with huge potential to unlock commercial value.

 

One of the biggest drains on profitability is the supply chain. Delays in analysis of incoming materials, eats into working capital. And, use of a material with an unacceptable level of impurity, because you could not test for it, is costly and potentially harmful to your reputation. From foundries, fabricators and metal component producers to electronics suppliers and recycling facilities, choosing the right technologies for every stage of the automotive development process is critical to ensure analysis keeps up with changing regulatory demands. Continued innovation and development is vital to help the automotive industry meet the challenges faced today and be well prepared for what’s to come.

 

About the author

Mikko Järvikivi is the Head of Global Product Management at Hitachi High-Tech Analytical Science.  With 15 years’ experience in material analysis and handheld instruments, Mikko joined Oxford Instruments in 2006, which was acquired by Hitachi High-Tech Group in July 2017. Mikko holds a M.Sc (Tech.) in Chemical Engineering from Aalto University in Finland.

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Fri. February 23rd, 2024

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