Effect of Processing Parameters on Microstructure and Mechanical Properties of an Al-Al 11 Ce 3 -Al 2 O 3 In-Situ Compos
- PDF / 854,652 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 36 Downloads / 258 Views
INTRODUCTION
FRICTION stir processing (FSP) for the microstructural modification of materials was developed based on the principle of friction stir welding (FSW).[1] Mishra and Ma have completed a comprehensive literature review on FSW and FSP.[2] In a recent review article,[3] Ma addressed the current state of the understanding and development of FSP. A variety of effective FSP applications have been shown, as follows: (1) homogenizing the microstructure of Al-based nanocomposites,[4,5] (2) producing Al alloys with an ultrafine-grained structure[6–8] and Mg alloys,[9] (3) fabricating a fine-grained superplastic microstructure,[10,11] (4) refining the microstructure of cast-aluminum alloys,[12–15] (5) forming a surface composite on an aluminum substrate,[16] (6) forming an in-situ metal matrix composite,[17–20] etc. It is widely recognized that the mechanical properties of metal matrix composites (MMCs) are controlled by the size and volume fraction of the reinforcements as well as the nature of the matrix-reinforcement interface.[21] Superior mechanical properties can be achieved when fine and stable reinforcements with good interfacial bonding are dispersed uniformly in the matrix. In conventionally produced particulate-reinforced MMCs, the size of reinforcement particles is normally much larger than 1 lm and the particles are located C.F. CHEN, Graduate Student, P.W. KAO, Professor, L.W. CHANG, Associate Professor, and N.J. HO, Professor, are with the Department of Materials and Optoelectronics Science, Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaoshiung 804, Taiwan R.O.C. Contact e-mail: pwkao@mail. nsysu.edu.tw Manuscript submitted February 17, 2009. Article published online December 2, 2009 METALLURGICAL AND MATERIALS TRANSACTIONS A
intergranularly in the metal matrix. Therefore, they cannot contribute to the strength by the Orowan mechanism. However, for composites with a large amount of nanometer-sized particles, which are distributed both intragranularly and intergranularly, the interparticle spacing may be reduced to the order of 100 nm or less, and the matrix grain size may be limited to the submicrometer range due to the Zener pinning effect.[22] The contributions due to the Orowan strengthening and the grain-size strengthening can then be very significant. In general, the reinforcing particles used in MMCs are formed prior to their addition to the matrix metal. In this case, the scale of the reinforcing phase is limited by the starting particle size, which is typically of the order of microns to tens of microns and is rarely below 1 lm. Other drawbacks for the conventionally processed MMCs that have to be overcome are poor interfacial bonding and poor wettability between the reinforcement and the matrix due to surface contamination of the reinforcements. A possible alternative is to synthesize the reinforcement in situ in the metal matrix.[23] Recent research work[17–19] has shown that in-situ aluminum matrix composites can be fabricated by FSP without a further consolidation
Data Loading...
