The Research On Microstructure And Properties Of SiC_p/MWCNTs Reinforced Magnesium Matrix Nanocomposites Fabricated By Accumulative Roll Bonding (ARB)

Pure magnesium is usually not used as structural material due to its poor strength and thermal stability. Magnesium matrix composites have been extensively applied in many fields, such as aerospace and light metal automotive applications, due to their low density and superior specific properties including strength, stillness and creep resistance.In present work, magnesium matrix nanocomposites were successfully fabricated through accumulative roll bonding (ARB). The selected reinforcements are nanosize-SiCp, MWCNTs and hybrid (SiCp+MWCNTs). After ARB process, the ARBed nanocomposites were warm rolled for further investigation. The microstructure and mechanical properties of nanocomposites are reported for various ARB cycles. To evaluate microstructure of the nanocomposites, the field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD) and transmission electron microscope (TEM) were applied. Mechanical properties were investigated through tensile and microhardness tests. Tensile tests were conducted at room temperature on servohydraulic universal testing machine, and the micro vickers hardness measurement was performed by using digital microhardness tester.For monolithic Mg, the bonding interfaces had not improved with ARB cycle. After ARB-2, the average grain size reached the minimum (2.3 ?m). After ARB-14, recrystallized grains, substructured grains and deformed grains accounted for 33.7%,64.3% and 2%, respectively. The intensity of (0 0 0 2) basal plane texture decreased with increasing of ARB cycles. After ARB-14 the (0 0 0 2) pole intensity of monolithic Mg was 15.5, which was slightly lower than that of raw Mg (15.8). With ARB cycles, c-axis of Mg tended to incline to RD. After ARB-14 the microhardness of monolithic Mg reached 67.6 HV, which was improved by 45.1% compared to raw Mg; UTS and YS decreased by 4.0% and 16.5% compared to raw Mg. After warm rolling, UTS and YS reached 276.7 MPa and 245.4 MPa, which were improved by 11.8% and 57.4% compared to raw Mg, by 16.5% and 88.6% compared to ARBed Mg, respectively.For Mg/nano-SiCp, the dispersibility of reinforcement and the interficial bonding of nanocomposite were better when the content of SiCp was 2 wt.%. After ARB-14, the average grain size of Mg/2 wt.%SiCp reached 2.6 ?m. During ARB process, incorporation of nano-SiCp promoted the recrystallization of Mg matrix, and the recrystallized grains accounted for 48.5% after ARB-14. After ARB-14 the (0 0 0 2) pole intensity of Mg/2 wt.%SiCp was 12.8, which was obviously lower than those of Mg/1 wt.%SiCp, Mg/4 wt.%SiCp and ARBed Mg. For Mg/nano-SiCp, the tensile property and hardness were better when the content of SiCp was 2 wt.%. After ARB-14, UTS and YS reached 291.2 MPa and 250.1 MPa, which were improved by 22.6% and 92.2% compared to ARBed Mg; E was improved by 203.3% compared to ARBed Mg. After ARB-14, the microhardness reached 80.5 HV, which was improved by 19.1% compared to ARBed Mg. After ARB-14, CTE of Mg/2 wt.%SiCp reached 23.9×10-6 ?-1,which confirmed that the incorporation of nano-SiCp improved the thermal stability of Mg matrix. After warm rolling, UTS and YS were further improved to 294.2 MPa and 254.5 MPa, respectively.For Mg/MWCNTs, the dispersibility of reinforcement and the interficial bonding of Mg matrix were better when the content of MWCNTs was 2 wt.%. After ARB-14, the average grain size of Mg/2 wt.%MWCNTs reached 2.4 ?m. During ARB process, incorporation of MWCNTs hindered the recrystallization of Mg matrix, and the recrystallized grains accounted for 17.7% after ARB-14. .During ARB process, MWCNTs activated the non-basal slip system of Mg matrix. After ARB-14, the (0 0 0 2) pole intensity of Mg/2 wt.%MWCNTs was 10.8, which was obviously lower than other materials. For Mg/MWCNTs, the tensile property and hardness were better when the content of MWCNTs was 2 wt.%. After ARB-14, UTS and YS reached 291.7 MPa and 257.1 MPa, which were improved by 22.8% and 97.6% compared to ARBed Mg; E was improved by 217.8% compared to ARBed Mg and by 4.8% compared to Mg/2 wt.%SiCp. After ARB-14 the microhardness of Mg/2 wt.%MWCNTs reached 89.8 HV, which was improved by 32.8% compared to ARBed Mg and by 11.6% compared to Mg/2 wt.%SiCp. After ARB-14, the CTE of Mg/2 wt.%MWCNTs (25.5×10-6?-1) was higher than that of Mg/2 wt.%SiCp. After warm rolling, UTS and YS reached 267.4 MPa and 235.8 MPa.For Mg/2 wt.%(SiCp+ MWCNTs), the dispersibility of reinforcement was better when the hybrid ratio was 7:3. The hybrid reinforcements further hindered the recrystallization of Mg matrix. When hybrid ratio was 5:5, the (0 0 0 2) pole intensity of nanocomposite reached 10.8 after ARB-14. The hybrid ratio had little effect on tensile property. The microhardness of nanocomposite increased with incrasing of MWCNTs ratio. When the hybrid ratio was 7:3, the CTE of nanocomposite was 23.9× 10-6 ?-1, which was situated between that of Mg/2 wt.% SiCp and Mg/2 wt.% MWCNTs. Based on the comprehensive properties, Mg/2 wt.%(SiCp+MWCNTs) has the best performance when hybrid ratio was 7:3, and the corresponding properties were as follows:UTS=294.9 MPa, YS=270.5 MPa. E=67.4 GPa. microhardness=89.4 HV, CTE=23.9×10-6 ?-1. After warm rolling. UTS and YS reached 270.8 MPa and 250.4 MPa.