The effect of multi-pass multi-directional forge(MDF)on the tribological properties of ZA22−xSi alloy(x=0,4,8 wt.%)was investigated.The results indicate that MDF breaks down the cast microstructure of alloys and produ...The effect of multi-pass multi-directional forge(MDF)on the tribological properties of ZA22−xSi alloy(x=0,4,8 wt.%)was investigated.The results indicate that MDF breaks down the cast microstructure of alloys and produces a well-modified microstructure comprising finely distributed α- and η-phases and primary Si particles.It is also found that,despite the matrix work softening,MDFed ZA22−xSi alloys show high wear resistance.The maximum wear resistance is observed in the five-pass MDFed ZA22−4Si sample,at the applied loads of 10 and 30 N,and its wear rates are lower than the wear rate of the as-cast ZA22 alloy by about 80% and 75%,respectively.MDF also significantly decreases both average friction coefficient and friction coefficient fluctuation of the sample.The high resistance of the substrate to microcracking,formation of hard Si reinforcements,fine redistribution of α- and η-phases in the microstructure,and formation of tribolayers rich in Al and Zn oxides can be considered as the main factors improving the tribological properties.展开更多
AZ61Mg alloy was multi directionally forged(MDFed) during decreasing temperature condition from 643 K to 483 K at a true strain rate of 3×10-3 s-1 up to cumulative strain of∑△ε=4.0 at maximum.A pass strain of...AZ61Mg alloy was multi directionally forged(MDFed) during decreasing temperature condition from 643 K to 483 K at a true strain rate of 3×10-3 s-1 up to cumulative strain of∑△ε=4.0 at maximum.A pass strain of△ε=0.8 was employed.While average grain size decreased gradually with increasing cumulative strain,the evolution of fine-grained structure strongly depended on the MDF temperature.Under the condition where the temperature was higher than the most adequate one,grain coarsening partially took place during MDF.In contrast,at lower temperature,inhomogeneous microstructure composed of the initial coarse and newly appeared fine grains was evolved.After straining over∑△ε=3.2(i.e.,over 4 passes of MDF) ,equiaxed ultrafine grains(UFGs) having average size of about and lower than 1μm were uniformly evolved.While the MDFed alloy to∑△ε=4.0 possessed relatively high hardness of HV 99,and it accepted further about 20%cold rolling almost without cracking.Because of the superior formability of the UFGed AZ61Mg alloy,the hardness was further easily raised to HV 120 by following cold rolling.展开更多
This work discusses tribological properties of commercial pure (CP) titanium processed by multi-directional forging (MDF) up to six passes at room temperature and 220 ℃. For this purpose, wear test was conducted by d...This work discusses tribological properties of commercial pure (CP) titanium processed by multi-directional forging (MDF) up to six passes at room temperature and 220 ℃. For this purpose, wear test was conducted by dry sliding pin-on-disk method on the initial and ultrafine grained samples using different stress magnitudes of 1, 1.5 and 2 MPa. The results showed that wear resistance of CP titanium increases after the first pass of MDF in comparison with the initial condition, irrespective of the applied normal stress. For example, the average wear rate of MDFed samples was decreased about 30% and 24%, after first pass at room temperature and 220 ℃, respectively. However, average wear rate of the samples processed by six MDF passes was reduced about 40% at lower normal loads;it was increased about 9% at higher ones as compared to the initial condition. It was also found that the dominated wear mechanisms were abrasive and delaminated at the lower stresses, while the delamination mechanism was intensified and a slight adhesion was observed during the higher applied normal loads.展开更多
Dynamic and static aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multidirectional forging（MDF） with decreasing temperatures from 410 to 300 ℃ and subsequent aging process. The result...Dynamic and static aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multidirectional forging（MDF） with decreasing temperatures from 410 to 300 ℃ and subsequent aging process. The results show that the morphology of the β-Mg17Al12 phases during forging process dynamically precipitates and aging process（statically precipitation） exhibited granular and laminar shapes, respectively. During the MDF, the inhomogeneous dynamic precipitation of the β-Mg17Al12 phases results in the uniformity on grain size, which is fine in the area with many granular Mg17Al12 phases but the grain is still coarse where there is no Mg17Al12 phases. During the aging process, the morphology of newly formed β-Mg17Al12 phases depends on the structural character of the forged sample. The newly precipitated β-Mg17Al12 phases are coarse laminar and needle-like shape in area with coarse grain. While, the fine newly precipitated β-Mg17Al12 phases are fine granular and needle-like in the area with fine grain.展开更多
文摘The effect of multi-pass multi-directional forge(MDF)on the tribological properties of ZA22−xSi alloy(x=0,4,8 wt.%)was investigated.The results indicate that MDF breaks down the cast microstructure of alloys and produces a well-modified microstructure comprising finely distributed α- and η-phases and primary Si particles.It is also found that,despite the matrix work softening,MDFed ZA22−xSi alloys show high wear resistance.The maximum wear resistance is observed in the five-pass MDFed ZA22−4Si sample,at the applied loads of 10 and 30 N,and its wear rates are lower than the wear rate of the as-cast ZA22 alloy by about 80% and 75%,respectively.MDF also significantly decreases both average friction coefficient and friction coefficient fluctuation of the sample.The high resistance of the substrate to microcracking,formation of hard Si reinforcements,fine redistribution of α- and η-phases in the microstructure,and formation of tribolayers rich in Al and Zn oxides can be considered as the main factors improving the tribological properties.
基金support given by the Light Metals Educational Foundation,Japan,and Ministry of Education,Culture,Sports and Technology,Japan,with Grant No.20560647
文摘AZ61Mg alloy was multi directionally forged(MDFed) during decreasing temperature condition from 643 K to 483 K at a true strain rate of 3×10-3 s-1 up to cumulative strain of∑△ε=4.0 at maximum.A pass strain of△ε=0.8 was employed.While average grain size decreased gradually with increasing cumulative strain,the evolution of fine-grained structure strongly depended on the MDF temperature.Under the condition where the temperature was higher than the most adequate one,grain coarsening partially took place during MDF.In contrast,at lower temperature,inhomogeneous microstructure composed of the initial coarse and newly appeared fine grains was evolved.After straining over∑△ε=3.2(i.e.,over 4 passes of MDF) ,equiaxed ultrafine grains(UFGs) having average size of about and lower than 1μm were uniformly evolved.While the MDFed alloy to∑△ε=4.0 possessed relatively high hardness of HV 99,and it accepted further about 20%cold rolling almost without cracking.Because of the superior formability of the UFGed AZ61Mg alloy,the hardness was further easily raised to HV 120 by following cold rolling.
基金supported financially by the Iran National Science Foundation (No.94809610)the Czech Science Foundation Project (No.GB 14-36566G)
文摘This work discusses tribological properties of commercial pure (CP) titanium processed by multi-directional forging (MDF) up to six passes at room temperature and 220 ℃. For this purpose, wear test was conducted by dry sliding pin-on-disk method on the initial and ultrafine grained samples using different stress magnitudes of 1, 1.5 and 2 MPa. The results showed that wear resistance of CP titanium increases after the first pass of MDF in comparison with the initial condition, irrespective of the applied normal stress. For example, the average wear rate of MDFed samples was decreased about 30% and 24%, after first pass at room temperature and 220 ℃, respectively. However, average wear rate of the samples processed by six MDF passes was reduced about 40% at lower normal loads;it was increased about 9% at higher ones as compared to the initial condition. It was also found that the dominated wear mechanisms were abrasive and delaminated at the lower stresses, while the delamination mechanism was intensified and a slight adhesion was observed during the higher applied normal loads.
基金supported by the National Natural Science Foundation of China (Nos.51204053,51674078 and 51374067)the Fundamental Research Fund for Central Universities (Nos.N160913002,N130409005 and N130209001)A Project supported by Scientific Research Fund of Liaoning Province (No.2015022003)
文摘Dynamic and static aging precipitation of Mg17Al12 phases in AZ80 magnesium alloy was studied by multidirectional forging（MDF） with decreasing temperatures from 410 to 300 ℃ and subsequent aging process. The results show that the morphology of the β-Mg17Al12 phases during forging process dynamically precipitates and aging process（statically precipitation） exhibited granular and laminar shapes, respectively. During the MDF, the inhomogeneous dynamic precipitation of the β-Mg17Al12 phases results in the uniformity on grain size, which is fine in the area with many granular Mg17Al12 phases but the grain is still coarse where there is no Mg17Al12 phases. During the aging process, the morphology of newly formed β-Mg17Al12 phases depends on the structural character of the forged sample. The newly precipitated β-Mg17Al12 phases are coarse laminar and needle-like shape in area with coarse grain. While, the fine newly precipitated β-Mg17Al12 phases are fine granular and needle-like in the area with fine grain.
