Case-A: Aluminum cross-section's response to the main criteria of bending stiffness - Considering two beams of steel and aluminum with somewhat equal or comparable yield strength, following are the observations for the aluminum section (Figure-c):
Stiffness: More than 1/3 of the steel beam
Max elastic displacement: more than 3X that of the steel beam
Energy; More than 3x elastic energy absorbed
Energy: More elastic + plastic energy absorbed
Weight saved: 64% - however, stiffness is still lower than for a steel beam.
Case-B: Response when the main criterion is Stiffness - Considering two beams, one of steel and one of Al, material yield strength is equal, followings are the observations (Figure- d, below):
Stiffness: equal to steel beam
Displacement: approx. 2.5x that of the steel beam
Energy: More than 6x elastic energy absorbed
Energy: Elastic + plastic energy absorbed: Much more
Weight saved: 40 - 50 %
Thus, we observe that aluminum and its alloy have good acceptability to the modern automotive design engineers owing to the fact that along with reduction in total vehicle weight, it also offers other benefits pertaining to vehicle safety, corrosion resistance, etc. The attribute of being comparatively lighter makes aluminum not only preferable to designers but it offers maneuverings and handling advantages to all sections of the product-business chain including design benefits, shop floor handling ease and other end user benefits. There is no doubt that aluminum alloys in all forms offer better design flexibility compared to other automotive application materials.
Besides the design aspects, other important issues which need to be considered for a prospective automotive material like aluminum alloy is the availability and efficiency of its manufacturing and processing technology. In general, Aluminum is one of the few metals that can be cast by any of the standard metal forming methods - die, sand, permanent mold, investment, plaster, continuous, lost foam, squeeze, and hot isostatic pressing. With the advances & innovations in manufacturing technology & processing procedures for quality castings, aluminum alloy is now poised to make further inroads in automotive applications. Component quality can now be enhanced easily by following approaches like - vacuum and pressure casting processes including permanent mould and semi-solid/squeeze casting and adopting automated inspection and non-destructive testing techniques (Bujalski, ). These diverse casting options along with the favorable design aspects and material characteristics are expected to have synergistic effects in augmenting the overall potential of aluminum alloy thereby making it a very viable and attractive substitute to steel for automotive applications.
4. Supply- Availability & Environmental Issues
There were some concerns regarding the availability and the industry's ability to keep on supplying and meeting the ever growing demands for aluminum materials. However, careful scrutiny reveals that there is no cause for concern, either with regard to the availability of materials required to produce aluminum, or the industry's ability to expand production capacity for meeting growing demands (EAA-Report). Aluminum is one of the most abundant elements on earth and the raw material used for production and processing of aluminum metal is predominantly bauxite and currently availability of bauxite ore is estimated to be over 40 thousand million tons, which is enough to last for more than 400 years at current rates of consumption (EAA, 1996). Presently, use of aluminum based products is very minimal and even considering a steady growth in consumption of automotive aluminum over the next 10 years the total percentage demand works out to be only 20%. Thus with the advances in production technology and manufacturing base and with such reserves of raw materials, availability and supply of aluminum will not be a barrier to wide-spread use of aluminum for automotive applications.
Aluminum use also offers a wide range of environmental benefits the most significant of which is reduction in automobile fuel consumption consequential to reduced vehicle weight resulting from its use. It also has superior corrosion resistance properties. Aluminum does not rust away on exposure to the environment like steel and its natural oxide coating blocks further oxidation. The risk of galvanic corrosion can be minimized by appropriate choice of alloy, component design, and protective measures. Another good property of aluminum is recycleability. It has substantial scrap value providing both economic and environmental benefits. More than 70% of automotive aluminum can be sourced from recycled metal (Aluminum Association Inc.) and importantly there is virtually no cycling limit as it doesn't loose its properties on recycling. Thus on these aspects too, aluminum stands out to be a very attractive alternative for automotive applications.
5. Costs & Other Factors
Initially, aluminum was not very cost effective but with technology maturing and infrastructures improving, cost issues can no longer remain a negative for aluminum compared to steel. For many automotive applications, aluminum is already in use and cost-wise it proves to be a better option. However for some components it doesn't enjoy a cost advantage over steel. But, there is reason to believe that with growing use, aluminum may find itself very cost competitive to steel and other materials. Another area of concern is the uncompetitive repair and maintenance cost of aluminum applications but this too should fade away with time and the development of better repair techniques and facilities.
There also are other factors which augment the prospects of aluminum for extended use in near future. Aluminum is found to offer a better quality finish and enables styling features that make it more acceptable to modern designers and new-age customers. Aluminum's lighter weight and stiffness can also enhance vehicle acceleration, handling, and reduce its noise, vibration and harshness characteristics.
