Interfacial Reaction in AZ91D Magnesium Alloy Matrix Composite Reinforced with Aluminum Borate Whisker

Abstract

AZ91D magnesium alloy reinforced with aluminum borate whisker (Al 18 B 4 O 33w , denoted by ABO w ) was fabricated by squeeze-casting. The heat treatment (T4) was carried out at 693 K in argon atmosphere for 48 and 96 hours, respectively, following water-quenched. The behaviors of interfacial reaction were studied in processes of fabrication and following heat treatment. Microstructures of interfacial reaction layers were investigated with transmission electron microscopy (TEM). Interfacial reaction layer in thickness of 5-10 nm was found in as-casted composite, and it was identified that the interfacial reaction layer was consisted of MgO. When the composite was heat-treated at 693 K for 48 hours, the surfaces of whiskers were covered with interfacial reaction layer completely and the thickness of interfacial reaction layer increased to about 20 nm. With increasing the time of heat treatment from 48 hours to 96 hours, the thickness of interfacial reaction layer on the surfaces of whiskers did not change obviously. The interfacial reaction layer was consisted of tiny MgO particles and a small quantity of MgB 2 particles. Although MgO particles played a good barrier to keep out of contacting between magnesium and whisker, the boundaries between MgO particles acted as a shortcut of magnesium atoms migration. Therefore magnesium could keep on reacting to whisker. The interfacial reaction could invade into the inner of whisker about 20 nm depth after the composite was heat-treated at 673 K for 96 hours. The surfaces of whiskers became wave-like because of interfacial reaction. An orientation relationship was found between MgO reaction layer and ABO w : ð11 1 1Þ MgO == ð320Þ ABOw and ½011 MgO == ½001 ABOw . The surfaces of MgO particles were consisted of close-packed (111) MgO plane.

Effects of Aging Treatment on the Bending Strength in AZ91D/Al<SUB>18</SUB>B<SUB>4</SUB>O<SUB>33w</SUB> Composite

“…9,10) So it is necessary to discuss the effects of interfacial reaction layer on fracture behaviors of composite. According to previous investigation, 20) the whiskers are wrapped completely with MgO interfacial reaction layer after solution treatment at 693 K for 172.8 ks. The interfacial reaction layer is consisted of tiny MgO particles and these MgO particles play a good barrier to keep out of interfacial reaction between matrix and whisker.…”

Fabrication and Characterization of AZ91/CNT Magnesium Matrix Composites

“…2b shows the discontinuously located chemical reaction products MgO(magnesia) with FCC structure exit on the interface of the between Al 18 B 4 O 33 whisker and matrix alloy. [10] Materials Science Forum Vols. 620-622…”

Aging Behaviors in AZ91D/Al<SUB>18</SUB>B<SUB>4</SUB>O<SUB>33w</SUB> Composite Fabricated by Squeeze Casting

“…It is thought that these interfacial precipitates are formed while the composite is conserved in stove at 473 K after squeeze casting. During following solution treatment, interfacial precipitates are dissolved and MgO interfacial reaction layer in thickness of 20 nm is formed, 21) as shown in Fig. 3(b).…”

“…21) Figure 4 shows HREM image of the interface between interfacial precipitate (Mg 17 Al 12 ) and ABO w in ascasted AZ91D/ABO w composite. The surface of whisker is smooth in atomic scale and is not covered with MgO particles.…”

“…[18][19][20] Moreover, magnesium can react to ABO w and forms MgO interfacial reaction layer in AZ91D/ABO w composite during heat treatment at 693 K. 21) At the same time, aluminum elements deoxidized from ABO w can dissolve into the matrix of AZ91D/ABO w composite. In order to optimize the aging treatment and provide the experimental and theoretical information for designing the properties of composites, it is significative to study aging behaviors of AZ91D/ABO w composite.…”