| There is considerable attention to in situ particle reinforced aluminum matrixcomposites by flux assisted synthesis (FAS) because of its simplicity, low cost and wellmatched interface between reinforcements and metal matrix. However, in spite of a longtime to study in situ aluminum matrix composites, the formation mechanisms of in situparticles and the essence of interface between reinforcements and matrix remain unclear. Inaddition, it easily produces some intermediate compounds in the preparation process ofcomposites by FAS. It still needs further exploration to get in situ particles with cleansurface.Recently, there is increasing attention to the preparation of in situ zirconium diboride(ZrB2) particles reinforced aluminum matrix composites. Firstly, the size of in situ formedZrB2is small. The nanoscale reinforcements can play a better role in refining as well as instrengthening than micron-sized particles. Moreover, the dystectic point and thermostableperformance of ZrB2particles can observably enhance the elevated-temperature mechanicalproperties of aluminum matrix composites. Hence, it is of great significance to lucubrate thepreparation of in situ ZrB2particles reinforced2024Al matrix composites.In this study, we aim to optimize the preparation process and rolling deformationprocess of in situ (ZrB2+Al3Zr) particles reinforced2024Al matrix composites, and someresults are given as follows:(1) Changing the addition sequence of KBF4and K2ZrF6has an effect on themicrostructures of composites. The interface boundaries of reinforcements and matrix ofcomposites fabricated with three addition sequences of salts are well without contamination.There is no obvious refinement in the composite with salt mixture of KBF4and K2ZrF6, butthe particles distribute homogeneously in the matrix. When KBF4is added first, the grainrefinement is remarkable, and the mainly reinforcements are rod-like Al3Zr with the size at a range of~3–15μm. When K2ZrF6is added first, the grain size of composite is slightly raised.However, the reinforcements are much smaller than those of composite with KBF4first.Tensile properties at room temperature reveal that the tensile strengthes of composite withKBF4first and with K2ZrF6first are better than that with salt mixture.(2) In situ ZrB2particles present typical hexagonal single and agglomerationmorphological features with the size of~0.2–1μm. In addition, there is quadrihedron-likeAl3Zr in the composite with K2ZrF6first. Apart from flower-like flakes, ZrB2particles alsogrow around the quadrihedron-like Al3Zr to form a ball-like agglomeration. Firstly, there arethree ZrB2particles growing along three directions of Al3Zr, respectively. Subsequently,more ZrB2grow on {0001}faces of ZrB2particles step by step to form a ball-likeagglomeration eventually. This growth pattern of ball-like agglomeration make themaximum exposure of {0001}basal planes of ZrB2, and that is beneficial to nucleationsubstrate for growth of α-Al.(3) There is significant influence of heat treatment process on the tensile properties ofrolling2024Al. When2024Al was rolled at350℃with total reduction of~85%and thenaged at160℃for12h, its tensile strength is only313MPa with elongation of8.6%. Whenthe treatment process is solid solution at450℃,470℃and490℃for50min respectivelyand then aging at160℃for12h, the tensile strength is353MPa,382MPa and394MPawhile elongation is20.0%,20.9%and21.6%. It reveals that solid solution is beneficial to thetensile properties of rolling2024Al. We also have a try in solid solution at495℃for30minand aging at the same process. It turns out that the tensile strength increases to436MPa withelongation of23.3%. |
PDF Full Text Request