Study On Fabrication, Microstructure And Properties Of FAC/AZ91Magnesium Matrix Composites

In this paper, FACs’ hollow-ball structure was used to modify theelectromagnetic shielding property. FACs/AZ91magnesium matrix composites withdifferent FAC particle content were fabricated by semi-solid stir casting. Byinvestigating the distribution of FACs in the matrix after different duration of stirring,the best process was determined. The micro-structure of the composites, the resultsof the distribution and the connection between the matrix and FAC were found. Thechange of the hardness, tensile and compress property caused by the addition ofFACs were tested. The friction property of the materials in different conditions wastested using cutting disc wear testing machine.The results showed that, FACs distributed uniformly in the matrix, and noobvious cluster was found. The alloy can go through the wall of the fly-ashcenosphere because of the existence of the hole and fill the ball. As the reacting withthe matrix, the structure of the fly-ash cenosphere was destroyed into fragment or thethickness of the wall was decreased. Compared with the matrix, the ultimate tensilestrength (UTS) and elongation (%) go up firstly and then decrease, which wasattributed to the addition of fly-ash cenosphere. The compressive strength increasedwith the increase of the cenosphere. The fracture of composites was brittle fracture.The wear property of composites were better than alloy AZ91. In different conditions,different wear form leaded the loss of the materials. Compared with the matrix, theshielding property of the composite didn’t show significant improvement as thecenospheres were destroyed.The surface of FAC particles were modified by reacting with Ca(OH)2, aftermodified, the surface of the cenosphere was covered by calcium silicate. Then themodified cenosphere were used to fabricate10wt%M-FACs/AZ91magnesiummatrix composites. The existence of the calcium silicate can keep the outer surfacefrom reacting with the matrix and maintain the structure. The outer surface of thefly-ash cenosphere was kept though the inside surface reacted with the matrix. Themechanical properties of the composites were tested. The results showed that therewas increase in the tensile strength but decrease in the elongation. During theprogress of wear, the loss of M-FACs/AZ91was less than AZ91but more than theFACs/AZ91because of the rise in amount.By adding the modified fly-ash cenosphere, the electromagnetic shielding property of the composite showed significant improvement in the frequency of30KHz~1.5GHz. After adjacent average, The SE of the composite was79-82dB,Which was2~10dB higher than the other two materials. When the frequency washigher, the SE of the M-FAC/AZ91was even better than the matrix. After alloyedand the addition of the FAC, the electrical conductivity of the composites were lowerthan pure Mg, the reflex of the electromagnetic wave was weaken, the key of betterelectromagnetic shielding property of the composites was the structure of FAC,which enhanced the absorb of the electromagnetic wave and the reflex inside thematerial. When the frequency is higher, the energy of electromagnetic waveincreased and the penetration also, leading the decrease in the electromagneticshielding property.