Material quality key to lightweighting

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It is vital to maintain material quality if you want to stay on the right track for vehicle lightweighting, says Mikko Järvikivi of Hitachi High-Tech Analytical Science

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 various metals that the industry is using across the supply chain and the technologies that are enabling the industry to ensure these materials meet quality and safety requirements.

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

The automotive industry will make up a quarter of all aluminium consumption (30 million tonnes) by 2025 and the average car will contain almost 100kg of aluminium replacing heavier parts.

A new generation of alloys is emerging, which could become integral to various components, combining low density, strength, stiffness and damage tolerance. Lithium is added to improve strength, and phosphorus and sulphur to improve machineability, but these can have a detrimental effect on corrosion resistance so must be added in small amounts.

As aluminium is enhanced, technologies are developing to provide effective materials analysis and enable manufacturers to improve quality control. Analysers should feature a high-performance spectrometer that enables the measurement of lithium in aluminium alloys and should be capable of measuring boron-aluminium alloys, which cannot be measured with any handheld XRF analyser. The preferred choice is a handheld LIBS, whilst OES can identify Li in Al, down to 0.0005%, as well as boron, phosphorus and sulphur.

Magnesium

Lighter than aluminium, magnesium has the highest strength to weight ratio of all structural metals. Abundant and easily recyclable, it has replaced steel and aluminium in some components and is used extensively in alloys.

Although magnesium is brittle and doesn’t have the creep resistance of aluminium, innovations could resolve that problem. Researchers can alter the microstructure of magnesium so it can be compressed at room temperature without cracking, and can also improve its energy absorption and ductility.

For analysis of alloys to the ppm level, OES gives the most precise results. The new generation of OES analysers are designed for fast, reliable and cost-effective analysis of all main alloying elements and identification of exceptionally low levels of tramp, trace and treatment elements.

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.

The road ahead

The pace of industry innovation brings crucial quality control challenges across the automotive supply chain and, in response, the field of materials analysis has been rapidly changing. The continued development and application of technologies like OES, XRF, LIBS and TA is making analysis easier, with huge potential to unlock commercial value. 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 current and future challenges.

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 holds a M.Sc (Tech.) in Chemical Engineering from Aalto University in Finland.