In this work, continuous conversion coatings on the surface of in situ TiB 2 particulate reinforced A356 composite were formed successfully by cerium surface treatment for the first time. Scanning electron microscope (SEM) analysis showed that the conversion coatings were inhomogeneous and could be divided into two types of regions, namely, fine crack region and noncrack region. Many cerium-rich nano-nodules were uniformly distributed in the whole coatings. Energy dispersive spectroscopy (EDS) analysis testified that the crack coatings mainly covered the interdendritic sites occupied by TiB 2 particulates and Si phases. X-ray photoelectron spectroscopy (XPS) analysis indicated that the conversion coatings were composed of CeO 2 , Ce 2 O 3 , Ce(OH) 4 , Ce(OH) 3 , and a little amount of Al 2 O 3 . The electrochemical polarization tests showed that the cerium-conversion treatment markedly improved the corrosion resistance of in situ TiB 2p /A356 composite in chloride environment, and the protection degree of the coatings was superior to that of conventional chromate-conversion coating. According to these results, the formation mechanism of cerium-conversion coatings was discussed.

In this work, the in situ TiB 2 particulates reinforced 2219 aluminium matrix composites were fabricated using the mixed salts method. The microstructural characteristics and mechanical properties of TiB 2 /2219 Al composites were investigated. The reults show that the composites reinforced with 5 and 10 wt-%TiB 2 exhibit higher Young's modulus, yield strength and ultimate tensile strength than the unreinforced matrix alloy. The improvement in strength may be attributed to strengthen mechanisms including dislocation strengthening due to the CTE difference between the matrix alloy and TiB 2 particulates, Orowan strengthening and load transfer.

Understanding the corrosion behavior of TiB 2p -reinforced aluminum matrix composites is crucial for their development as effective composites. In this work, corrosion characteristics of in situ TiB 2 particulate reinforced Al-Si alloy (A356) composite after T6 treatment are investigated by electrochemical techniques. The electrochemical impedance spectroscopy (EIS) reveals that the protection of nature film for the composites is worse than that for A356 alloy. Polarization experiments testify that the composites are susceptible to corrosion compared with their matrix alloys. Moreover, the corrosion resistance of the composites markedly decreases with increase in the TiB 2 content. The observations of the corrosion morphologies after polarization test show that the corrosion primarily occurs at the interdendritic sites with a large amount of TiB 2 particulates. Corrosion progress continues into the composite inner along the regions of a-Al dendrite. The poor corrosion resistant properties of the composites are considered primarily due to the galvanic corrosion between noble TiB 2 reinforcements and more active aluminum matrix, as well as the weak protection of the defective nature film on the composite.

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