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In this contribution, authors present a review on the state-of-the-art in the utilization of industrial and agricultural waste materials for the development of metal-matrix composites (MMCs), providing, through the judicious analysis of an ample and varied references source -from the oldest to the newest ones -, an insight into the challenges and opportunities for the exploitation to their full potential. In addition to its topicality, the novelty of this contribution lies in the presentation of key statistical, technical and property-related information of a comprehensive variety of waste materials classed into two main groups, namely, fly ash reinforced MMCs and MMCs derived from other waste materials. Although fly ash has been exploited in a broad range of applications, the attention paid for its use in the development of MMCs seems to be insufficient. A purposely designed chart helped to pinpoint the more demanding and profitable applications of fly ash, and establish strategic opportunity areas. With the exception of the recent utilization of fly ash for the automotive industry, virtually no other waste material has been reused for a specific industrial application. In this context, by identifying five reasons for this Downloaded by [University of Nebraska, Lincoln] at 08:41 26 August 2015 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 observed delay, an essential goal of this review is arouse the interest of academicians, scientists/technologists and industrialists in the use of those materials for the fabrication of MMCs. In the case of agricultural materials, a two-fold perspective may apply, because while on the one hand, certain chemical elements have to be removed for specific applications, on the other hand, recovery of certain elements might be more attractive. Based on the significant progress observed so far, in terms of scientific and technological research, a promising future can be anticipated. The proper use of industrial and agricultural waste materials entails knowledge generation as a prerequisite for incubation of pilot-plant and industrialization stages, culminating with all related benefits to society.

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The effect of magnesium and silicon additions to aluminum, free silicon on the SiC substrate, nitrogen gas in the atmosphere, and process temperature on the wetting characteristics of SiC by aluminum alloys are investigated using the sessile drop technique. The contribution of each of these parameters and their interactions to the contact angle, surface tension, and driving force for wetting are determined. In addition, an optimized process for enhanced wetting is suggested and validated. Results show that the presence of free silicon on the surface of SiC significantly reduces the contact angle between the molten alloy and the substrate. The positive effect of silicon on the contact angle is attributed to a chemical reaction in which both SiC and aluminum are active participants. The results also indicate that nitrogen gas in the atmosphere positively influences the liquid/vapor surface tension, and the presence of magnesium in the aluminum alloy favorably affects the overall driving force for wetting. A mechanism is proposed to explain the beneficial role that the interaction of nitrogen with magnesium plays in enhancing wetting. Magnesium significantly reduces the surface tension of aluminum melts but has a low vapor pressure. Consequently, it readily volatilizes during holding at the processing temperature and is lost from the alloy. It is proposed that a series of chemical reactions in the system Al-Mg-N are responsible for reintroducing magnesium into the melt, thus, maintaining a low melt surface tension. Interactions between the aluminum alloy and the silicon carbide substrate that may lead to the dissolution of the substrate and the formation of undesirable reaction products, particularly Al 4 C 3 , are examined, and means for mitigating their formation are outlined.

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