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Recyclable aluminum rolled products building blocks for a sustainable world
Abstract
Recyclable rolled products is expected to play a major role towards a future sustainable world, providing a number of benefits to all the manufacturers of rolled aluminum products. It is logical to increase the amount of recycled aluminum from an energy efficiency standpoint, particularly when energy costs are high. Recycling has the advantage of capturing the embedded energy and the environmental benefits associated with the scrap metal. Recycled aluminum is vital to the nation's economy and it minimizes the need for imported metal, cuts down costs and emissions. Recycled aluminum can also be rolled into other alloys to form additional building blocks of materials for use in transportation, packaging, building, and construction. Aluminum can be recycled with large energy and emission savings and essentially without any loss of physical, chemical or mechanical properties. This advantage is so dominant for aluminum that it has become a key factor in its sustainability as an industry.
Recycling of aluminum is beneficial due to reduced energy inputs, greenhouse gas emissions and raw material costs. Beverage cans are currently the second largest source of old scrap, and could become even larger with improved collection. However, impurities such as iron, titanium or lead may impede end-of-life recycling at higher levels, especially in closed-loop systems where they can accumulate over time. A generic material flow model for impurity accumulation in a simple recycling system is presented here. Sensitivity analysis was used to investigate the effect of key parameters on dynamics of accumulation and concentration at steady state. It was found that it takes longer to reach steady state at high collection rates, and that the steady state concentration is disproportionally higher. Increasing the U.S. beverage can collection rate from today’s 54% to the goal of 75% may cause more than a doubling of impurity concentrations unless better scrap treatment and remelting are developed in parallel or the scrap is used in other applications.
In the present study, the fabrication of an Al-based metal matrix composite material obtained directly from the melting of the aluminium used beverage cans in a modified rheocasting process is presented. The analysed operational condition is the shear rate applied to the bath and its influence on the properties of the obtained samples. Additionally, samples were heat treated at two different times. The characterization of the phases obtained in Al-based MMC was made by means of metallography, scanning electron microscopy with energy dispersive spectroscopy and electron microprobe with wavelength dispersion spectroscopy. The results show that some constituents were formed during the fabrication process of the MMC, mainly Al6(Fe, Mn), which are partially transformed during the heat treatment. Additionally, samples were evaluated using dynamic mechanical analysis, and the results suggest that the obtained MMC could have very good mechanical properties, similar or superior to the aluminium alloys commonly used for structural applications such as 6XXX family.
The aluminum industry is a leading proponent of global sustainability and strongly advocates the use of recycled metal. As the North American primary aluminum industry continues to move offshore to other geographic areas such as Iceland and the Middle East, where energy is more readily available at lower cost, the importance of the secondary (i.e., recycled metal) market in the U.S. will continue to increase. The purpose of this paper is to take an integrated, industry-wide look at the recovery of material from demolished buildings, shredded automobiles, and aging aircraft, as well as from traditional cans and other rigid containers. Attempts will be made to assess how the different alloys used in these separate markets can be recycled in the most energy-efficient manner.
With the advent of modern magnesium alloy technology, magnesium alloys have found applications as diverse as jets, helicopters, inline skates, and vascular stents. General Dynamics' latest military amphibious vehicle for the U.S. Marines, the Expeditionary Fighting Vehicle (EFV), includes magnesium in its complex transmission casings. The main magnesium alloy being evaluated for the EFV is Elektron 21, a new sand or investment casting alloy combining castability, corrosion performance and the ability to operate at high temperatures.