真空压力浸渗制备SiC_(p)/AZ91复合材料的显微组织、力学性能和磨损行为

采用真空压力浸透法制备SiC_(p)/AZ91复合材料,研究其显微组织、力学性能和耐磨性。结果表明,SiC颗粒均匀分布于金属基体中,并与基体界面结合良好。Mg_(17)Al_(12)相在SiC颗粒附近优先析出,SiC与AZ91基体的热膨胀系数失配导致高密度位错的产生,加速基体的时效析出。与AZ91合金相比,SiC颗粒的加入提高了复合材料的硬度和抗压强度,这主要是由于载荷传递强化和晶粒细化强化机制。此外,由于SiC具有优异的耐磨性,在磨损过程中形成稳定的支撑面保护基体。

Towards relieving center segregation in twin-roll cast Al-Mg-Si-Cu strips by controlling the thermal-mechanical process

Serious center segregation greatly limits the application of twin-roll casting(TRC)technology for produc-ing 6xxx alloy strips.Herein,Al-0.9Mg-0.6Si-0.2Cu-0.1Fe(wt.%,6061)strips with different thicknesses were fabricated by TRC,and we found that the center segregation was well relieved with the thick-ness increased from 3 mm to 4 mm.To reveal the mechanisms of mitigation of center segregation in the 4 mm strip,various techniques including solidification simulation,crystallographic calculation,elec-tron backscatter diffraction(EBSD),and electron probe micro-analyzer(EPMA)were utilized.The re-sults disclosed that the Fe-containing phase in the 3 mm strip wasπ-AlFeMgSi,while the counterpart in the 4 mm strip wasα-AlFeSi.Theα-AlFeSi could serve as nucleation substrates for Mg_(2)Si and Q-AlCuMgSi phases,thus promoting the uniform distribution of elements and preventing the accumulation of phases in the center region.Three matching planes between theα-AlFeSi and Q/Mg_(2)Si were exam-ined as:(1120)_(α-AlFeSi)//(0001)_(Q),(0001)_(α-AlFeSi)//(110)_(Mg2Si),and(1120)_(α-AlFeSi)//(110)_(Mg2Si).Meanwhile,the smaller roll separating force during the TRC process in the 4 mm strip could weaken the force-induced liquid flow behavior in the semi-solid region,which is the other reason for the alleviation of center seg-regation.Owing to the elimination of the center segregation,a more excellent fracture elongation was achieved in the as-homogenized 4 mm strip(∼29%)compared with the counterpart of the 3 mm strip(∼20%).This work may provide a strategy to eliminate the center segregation,thus further promoting the application of TRC process and producing high-performance Al alloy strips efficiently.

Effect of large thickness-reduction on microstructure evolution and tensile properties of Mg-9Al-1Zn alloy processed by hard-plate rolling

The effect of large thickness-reduction on microstructure evolution and tensile properties of Mg-9 Al-1 Zn alloy(AZ91)processed by hard-plate rolling(HPR)was investigated.Increasing rolling reduction from55%to 85%increases the volume fraction and refines average size of fine grains(<3μm,FGs),leading to an optimized bimodal-grained structure consisting of coarse grains(CGs)uniformly embedded in FG regions.The sample with 85%reduction exhibits the highest yield strength of~314 MPa,ultimate tensile strength of~381 MPa and elongation of~11%.The high strength is primarily due to the contribution of grain boundaries(GBs)strengthening by FGs(accounting for~65%of strength),meanwhile the improved ductility originates from the optimized bimodal-grained structure and weakened basal texture that favor a higher ductility.The present findings successfully overcome the trade-off dilemma that the largereduction rolling processing on Mg alloys usually enhances strength at expense of ductility.In addition,the intensified heterogeneous deformation and favorable formation of a bimodal-grained microstructure during large-reduct ion HPR was addressed by tracing micro structure evolution details in grains of intere st via quasi-in-situ electron back scattering diffraction(EBSD).The present study can be instructive for further designing novel Mg alloys by tailoring bimodal-grained structures for superior combination of mechanical properties.

Balancing the strength and ductility of Mg-6Zn-0.2Ca alloy via sub-rapid solidification combined with hard-plate rolling

In this study,we successfully prepared a Mg-6Zn-0.2Ca alloy by utilizing sub-rapid solidification(SRS)combined with hard-plate rolling(HPR),whose elongation-to-failure increases from~17%to~23%without sacrificing tensile strength(~290 MPa)compared with its counterpart processed via conventional solidification(CS)followed by HPR.Notably,both samples feature a similar refined grain structure with an average grain size of~2.1 and~2.5μm,respectively.However,the high cooling rate of~150 K/s introduced by SRS modified both the size and morphology of Ca_(2)Mg_(6)Zn_(3) eutectic phase in comparison to those coarse ones under CS condition.By subsequent HPR,the Ca_(2)Mg_(6)Zn_(3) phase was further refined and dispersed uniformly by severe fragmentation.Specially,the achieved supersaturation containing excessive Ca solute atoms due to high cooling rate was maintained in the SRS-HPR condition.The mechanisms that govern the high ductility of the SRS-HPR sample could be ascribed to following reasons.First,refined Ca_(2)Mg_(6)Zn_(3) eutectic phase could effectively alleviate or avoid the crack initiation.Furthermore,excessive Ca solute atoms inα-Mg matrix result in the yield point phenomenon and enhanced strain-hardening ability during tension.The findings proposed a short-processed strategy towards superior performance of Mg-6Zn-0.2Ca alloy for industrial applications.