Ever since automobile first came into being, body materials ranging from steel, iron and other metals to plastics, composites, and even wood have been jockeying for the position of the main structural material of the automobile. A few decades back, aluminum joined the race and very soon with its superior properties and characteristics, became a favored choice of automobile makers. Today, it is touted as the material of choice for advanced, next-gen vehicles from electrics to pick-up trucks.
Steel however continues to be the world’s most important and useful engineering material. What makes it so is it is highly ductile, malleable, tensile, corrosion-resistant, and above all, sports a shiny luster. When alloyed with small amounts of other metals, steel can acquire any characteristic that is needed. As far as metal consumption is concerned, steel continues to be the numero-uno, with China alone accounting for over 50% of global steel production.
On the other hand, Aluminum is a soft and lightweight metal with a dull-silvery appearance that stems from a thin layer of oxidation forming quickly when exposed to air. Non-toxic, non-magnetic, and non-sparkling, Aluminum in recent years has become the second-most consumed metal globally.
STEEL VS AUTOMOBILE IN AUTOMOBILE INDUSTRY
Although aluminum has been used for several years now in automobiles, its proportion in newer vehicles has increased steadily in recent years. The one factor where it has been scoring over steel is its lower density which makes it lighter than steel. Despite being lighter, aluminum is as strong as steel.
In an age where climate-change has become a cause for concern, fuel efficiency and carbon emission targets have become the norm the world over, and lighter fuel efficient vehicles, the favored customer choice. This is what is compelling the automobile industry to gravitate towards aluminum. Lighter fuel-efficient vehicles translate to lower fuel consumption, improved acceleration, better braking, and easier handling, supplemented by better fuel economy and significantly lower carbon dioxide emissions. According to a leading US consultancy, Ducker Worldwide, aluminum remains the fastest growing automotive material over competing materials and is entering its most unprecedented growth phases since the tracking of the shifting mix of automotive materials.
Despite the sudden shift towards aluminum, most car companies continue to rely heavily on steel which remains the dominant material in automobile manufacturing accounting for roughly 60% of the weight of an average automobile, making up the body frame, propeller shaft, seat frame, and exhaust tubes of modern cars. The reason for the continued dominance being that steel has the capability to withstand the extreme pressure generated by the car. Further it possesses exceptionally high torsional rigidity and is far cheaper than aluminum.
HOW DO THEY COMPARE?
Among the most commonly used materials in the manufacturing industry, aluminum and steel share certain similarities in terms of appearance, but otherwise are different in many ways with own unique characteristics.
In what ways they are different is best summed up in the following ways.
WEIGHT
Steel weighs more than aluminum as it’s stronger and more durable. Essentially 250% times denser than aluminum, steel is obviously heavier and due to its high density / weight, is less likely to bend under force or heat. On the other hand, Aluminum is extremely light-weight and half as dense as iron.
However, it is shape and structural rigidity that contributes to the strength of a structure. When it comes to that and when the two factors are optimized, aluminum is what provides similar reliability to a comparable steel structure at just half the weight. This means that aluminum made automobile can be built at a given strength that is two-thirds the weight of comparable steel built one. A good example of this are automakers like Tesla and Ford whose automobiles have aluminum bodies that translates the weight savings to the battery or payload capacity.
However some experts disagree. They point out that the body and chassis make-up half the weight of the average vehicle, and so material can make a huge difference in weight, stiffness, and strength of the vehicle. Herein, the tensile strength of steel is up-to 2,000 MPa (290,000psi) which is about four times stronger than the strongest aluminum alloys available today. The tensile strength difference means that aluminum parts need to enhance thickness to meet safety standards.
Automobile manufacturers will need to drastically reduce the weight of vehicles to meet the reduced fuel emissions criteria and GHG requirements. Herein, some automobile makers are gradually increasing the use of aluminum alloys as the first and main solution to make vehicles lighter. Likewise, some others are using advanced high-strength steels (AHSS) for their vehicles.
Overall, despite improvements, Steel still cannot compete with Aluminum when it comes to automobile light-weighting, especially in heavy passenger vehicles – SUVs and light trucks. Further, apart from a few critical areas pertaining to the safety of the passenger cabin (like longitudinal front, roofrail, and upper), an entire body-in-white from aluminum can be made. This will result in significant weight reductions and improved vehicle performance.
To be acceptable, it is extremely important, lightweight solutions need to be adopted into the vehicle design only if they do not compromise on quality, comfort, safety, or competitiveness.
The lightweight of the aluminum is still a work-in-progress that continues to be a hot topic in the automobile world and likely to do so through the next decade according to some experts.
STRENGTH
When it comes to strength, Steel is the undisputed winner. Further it is harder than aluminum, despite being at risk for corrosion.
Though aluminum is also strong and increases its strength in colder environments, it is more prone to dents and scratches than steel. On the other hand, steel is less likely to warp or bend from weight, force, or heat, which is why it remains one of the most durable industrial materials. However, aluminum does not become brittle at low temperatures; in fact, the strength of aluminum increases when cold.
Despite factoring in strength attributes, some experts feel that aluminum-bodied vehicles are far safer than their steel counterparts. This is attributed to better energy absorption, larger crush zones that fold more predictably and larger overall size.
On the other hand, some experts affirm that the material does not matter as much as how the material is designed. A safe vehicle for that matter can be designed with other materials than steel, but overall it is a combination of materials and design that is vital for the automobile safety.
Even though the newer, higher-end vehicles like luxury vehicles are made from aluminum like Ford with its F-150 frames (manufacturer claims that the aluminum’s lightweight properties make it ideal for use in frames for it encourages greater fuel efficiency), the majority of cars and trucks on the road continue to feature steel frames for its stronger and more durable than aluminum.
Overall, it is still unclear whether the aluminum frames (aluminum can be as safe as steel, but at a higher cost) will take off strongly since steel continues to stay as the most dominant metal in automobile manufacturing, in the strength category.
SUSTAINIBILITY
Though aluminum can be easily recycled through advanced processes, steel continues to be the most recycled material in the world.
Further, steel recycling process is simpler. This is attributed to its ferrous property that allows for easy scrapyard sorting. Moreover all alloys of steel can be melted together and remixed to produce any alloy of steel. On the other hand, aluminum is costlier to recycle for it involves separation of different aluminum grades before melting in order to preserve the grades.
WORKABILITY
Aluminum is light-weight as well as extremely flexible, which means that it can flex under load and bounce back from the force of impacts. This makes it extremely easy to work with. On the other hand, steel is heavy and mostly inflexible which makes it difficult to work with. Even some grades of AHSS (advanced high-strength steel) can be challenging to work with, despite being known for higher yield and ductility than aluminum.
Though aluminum is lighter and flexible, there are many cases of notable automobile body designs that would not be possible with aluminum due to its lower ductility and lower elongation which are indications of formability; one such is Cadillac body design. Other example is that of GM (GENERAL MOTORS) body closure panels, which were designed for aluminum as they were of lower mass. Months later, they were replaced with steel due to cost factor, the mass was removed another way, either from the steel components or in other areas.
Chevrolet Silverado was predicted to follow in the footsteps of FORD F-150, but later the whole aluminum shift part of it was shelved and today it uses aluminum for only the swing panels, hood, doors, and tailgate.
MALLEABILITY
Aluminum is extremely flexible, elastic, and malleable. It can be extruded either hot or cold and into any desired shape just by passing it through a die. Further, it can also be manipulated through bending and forming operations.
On the other hand, steel though extremely durable and resilient is also extremely rigid. This makes it susceptible to cracks or rips if pushed too far during the spinning process.
So as far as malleability factor goes, the advantage lies with aluminum for its excellent malleability and smooth fabrication allows it to form deep, intricate and precise spinnings. This in turn gives the handlers significant design freedom.
CONDUCTIVITY
Aluminum is an excellent conductor of heat and elasticity. For instance, an aluminum conductor weighs around half the equivalent copper conductor with the same conductivity. Also, aluminum is a good reflector of both light and heat which steel is not.
CORROSION RESISTANCE
Aluminum reacts with the oxygen in the air to form a microscopically thin layer of oxide; this layer is only 4 nano-metres thick but provides excellent protection against corrosion. Further, it even repairs itself if damaged.
Another added benefit is that aluminum oxidizes via the same type of chemical reaction that causes iron to rust. But unlike iron oxide, aluminum oxide sticks to the metal, shielding it from decay. As a result of this factor, aluminum does not require paint or other coating to keep it from rusting.
On the other hand, Steel typically needs to be painted after being spun in order to protect it from rust and corrosion. However there are certain types of rust-resistant steel, known as stainless steel that typically contain small concentrations of alloy metals like chromium to protect against corrosion.
COST
The cost of aluminum and steel are constantly fluctuating based on global supply and demand, related fuel costs, and the iron and bauxite ore market.
Even with the fluctuations, a pound of steel is said to be cheaper than a pound of aluminum.
SO, WHERE DOES IT GO FROM HERE?
In the climate-change era, automakers the world over are compelled to compete under ever-tightening fuel economy and emission guidelines. Squeezed on both sides, the automakers are being pushed to manufacture lighter vehicles by efficiency guidelines while forced by safety guidelines to make stronger, stiffer, bigger vehicles. These factors in turn are driving automakers to use aluminum more than steel.
Newer grades of steel however can compete on mass reduction and outperform the other materials. The third generation of AHSS (advanced high-strength steel) having micro-structures on the scale of nano-metres (NANO STEEL) is smaller than those found in traditional steels. This allows it to provide the high-strength required by automotive engineers as well as significant ductility (the strongest available steels with the formability of mild steel). Overall, an AHSS that does not sacrifice on strength but offers high ductility would be ideal for reducing weight, whilst maintaining stiffness.
POINT however is that the automakers need to compete under ever-tightening fuel economy guidelines.
The future runs on the fact – the automobile manufacturers will need to persuade buyers that they are buying secure and more technically advanced vehicles compared to earlier models.
This is where that AHSS cannot compete successfully with aluminum alloys in the automotive industry for weight reduction reasons, especially in bigger vehicles category like SUVs, trucks, etc. Likewise, every aluminum intensive car and truck crash tested in the US has earned the highest 5-star safety rating. More importantly, consumers have expressed satisfaction in terms of its fuel economy as well as the overall performance, durability, and safety.
VERDICT is that tensile strength, ductility, and cost considerations will lead a vehicle’s body and exterior to stay heavily reliant on AHSS as well as aluminum alloys now and in the future. Likewise, semi-structural interior and power-train components will create more opportunities for magnesium and composites.
In general, the use of aluminum and other light materials will be predominant in heavy vehicles like pick-ups and SUVs. Likewise, AHSS is likely to stay dominant in light and small vehicles like VW Golf 7. Over the long term (beyond 2025), cars will most likely use a multi-material mix, combining varied types of AHSS steel, aluminum alloys, carbon fibre, magnesium, plastics, mild steel, and other materials, to achieve the weight, cost and performance targets.
On the whole, ONE thing will be clear – despite aluminum making big forays, no material will ever achieve the dominance that mild steel enjoyed in the past. The new category of steel in the offing – ‘NANO STEELS’ will in the near future likely compete with 7075 and 7049 aluminum alloys, in properties (specific tensile strength and ductility).
All said and done, the battle between the aluminum and steel will continue to go on.
RIGHT SOURCE FOR ALUMINUM COMPONENTS
If you’re looking to purchase aluminum components, then look no further than SBMI Group based out of Hyderabad, India; this Group diversified portfolio comprises segments ranging from aluminum / manganese components to fan manufacturing, and retail.
One of its division, Sri Balaji Metal Industries, is a leading high-performance; high-quality aluminum and magnesium ingot manufacturer (one of the biggest non-ferrous alloy manufacturers in SOUTH INDIA); it presently manufactures 35+ different grading GDC & PDC alloys.
The company’s magnesium die-cast casting components offer easy machinability, good thermal and electrical conductivity, thin-wall and complex parts applications, noise and vibration dampening, finishing, and above all, full recycling capability.
The company’s extensive portfolio of aluminum and magnesium components offers superior mechanical properties meets specific & stringent quality criteria requirements that caters to the overall customer-satisfaction. All the alloys undergo stringent quality checks to match the complex compositions & specifications of the customer.
There are two more divisions –
Sree Padmavati Metal Industries, which has one of the biggest aluminum dross processing unit (a one of a kind state of the art facility) processes aluminum dross and recover metal.
Gaglani Die Casting deals in High-Pressure Die Casting and aluminum pressure die cast components.
You can count on these companies to meet all of your aluminum metal requirements!!!!!