Abstract: In this paper, continuous carbon fiber reinforced aluminum matrix (Cf/Al) composite plate with complex curved surface is fabricated by liquid-solid infiltration extrusion. The influence of fabrication parameters, such as the melting temperature, extrusion temperature and extrusion pressure on the Cf/Al composite plate is studied. The experimental results show that the liquid-solid infiltration extrusion process can be used to fabricate the Cf/Al composite with curved surface. The Cf/Al composite exhibits good infiltration and well-formed quality when the extrusion pressure is 50MPa, the extrusion temperature is 670°C and the melting temperature is 690°C. According to the microstructure observation, the carbon fiber uniformly distributes in the aluminum alloy matrix without damage and obvious defects. The density of the composite is decreased by 17.9%, from 2.71g/cm3 to 2.29g/cm3, which is lower than that of the matrix alloy, and the ultimate tensile strength is increased by 120% compared with the matrix alloy, from 127MPa to 279MPa.
Abstract: In this paper, the microstructure and mechanical properties of thixoformed 1973 (AlZn5.5Mg2.4Cu1.7Zr) wrought aluminium alloy were investigated. A cooling slope was used to produce non-dendritic billets. Thixoforming process parameters were determined as follows: die temperature of 250 °C, feedstock temperature of 600 - 605 °C, punch velocity of 7 mm/s. Mechanical properties of thixoformed with ultimate strength of 461 MPa and elongation of 3,1 % in the T2 condition. The lower properties of the thixoformed material are mainly associated with porosity.
Abstract: Semisolid slurries of four wrought alloys were fabricated via partial melting of commerical wrought aluminum alloy. Thixoforming experiments of four typical parts were performed. The results showed that a large amount of equiaxed grains before soaking in semisolid state were created due to recrystallization occurred in the continuous heating from room temperature to a given temperature above recrystallization temperature. It provides a desirable microstructure to form spheroidal grains during the next soaking process in semisolid state. The microstructure of the 2A12,7A04 and 7075 semisolid slurry consisted of fine and spheroidal grains. The elongation of the thixoformed parts were higher those of the hot-rolled plate. The UTS of the thixoformed parts were close or ever higher than those of the hot-rolled plate. Although the grain size and roundness of the 5A06 semisolid slurry are not very desirable, the mechanical properties of the thixoformed part are close or ever than those of the hot-rolled plate. The high mechanical properties of the thixoformed parts further confirmed the feasibility of short-process thixoforming route
Abstract: The microstructure and mechanical properties of 7050 alloy rheo-castings after treated by Annular Electromagnetic Stirring (A-EMS) melt treatment were investigated. The results revealed that, under A-EMS, the refinement and homogeneity of the solidification structure could be improved greatly and the slurry was suitable for the following rheo-casting; and also the hot-cracking defects in the casting process were significantly alleviated, meanwhile, the strength and ductility of the alloy casting were found to be comparable to those of conventionally forged 7000 series alloys.
Abstract: Al–Si A413 treated and untreated alloys were cast and poured at approximately 720 oC, 700 oC, and 680 oC in a cooling slope to obtain the semisolid material feeding the ceramic nozzle (150 cm3) at the lower roll (single-roll melt-dragged processing)—this drags the metallic slurry via the chill/columnar layers at a rate of 0.2 m/s, forming a molten-metal strip with a thickness of 2 mm and width 45 mm, approximately. The untreated alloy poured at 720 oC formed coarse structures of α-Al dendrites, as well as a coarse eutectic of Al–Si and microshrinking on the surface of the casting strip facing the atmosphere. The Al–Si 413 alloy poured at 680 oC and treated with Al5Ti1B (0.1%) led to microstructural refinement, resulting in α-Al globular structures, the absence of microporosities on the surface facing the atmosphere, and a finer and more homogeneous distribution of the eutectic grains with smaller Si particles. The AlTiB master alloys are not used as a grain refiner in Al–Si alloys because of Si poisoning. This subject is discussed in this paper. The addition of the inoculant and 0.2% of the Al–Si eutectic morphology modifying agent (Al–10%Sr) refined both the α-Al and eutectic phases more efficiently in the cast strip poured at 700 oC and 680 oC. This suggests that the inoculant did not interfere with the action of the modifying agent. As a result, molten metal strips of higher mechanical strengths and ductilities were obtained.
Abstract: In this study, ZL104 aluminum alloy supplied in cold rolled state was introduced in recrystallization and partial melting (RAP) process to fabricate semi-solid billets. During the RAP process, samples cut from cold rolled ZL104 aluminum plate were heated to different semi-solid temperatures, and the effects of isothermal treatment parameters on the microstructures of semi-solid billets were investigated. Results showed that, with the increase of isothermal holding temperature and time, both the average grain size and the shape factor were increased. Namely, the shape of solid grain was more and more spherical, but the size of solid grain was larger and larger, which may be not suitable for semi-solid forming. The size of liquid droplets was increased while the number of liquid droplets was decreased with increasing the isothermal holding temperature and time. Microstructural coarsening of solid grain were attributed to coalescence and Ostwald ripening mechanisms, however, the latter one played a more and more important role with the increase of isothermal holding time and temperature. Additionally, The optimal isothermal holding temperature and time are 570 °C and 5 min, respectively, and the coarsening rate constant is 1357.2 μm3/s at 570 °C.
Abstract: Ultrasound treatment is one of the known method to obtain the globular microstructure for semisolid processing of aluminum alloys. Notwithstanding the numerous advantages, the main industrial limit of this method is the low service life of the horn due to the combined hot corrosion and erosion phenomena. Various approaches are reported in literature to overcome this problem, but a real satisfactory option does not seem to be available yet. In this paper, the behavior of a H11 tool steel sonotrode coated with a thin layer of TiAlCN is investigated and compared with the performance of an uncoated steel one. The lifetime of the horn was evaluated in terms of effectiveness in semisolid feedstock material preparation. For this purpose, the microstructure of semisolid cast samples obtained after different working times was analyses by optical and scanning electron microscopy. Moreover, melt contaminations due to the probe dissolution were also evaluated. The applied coating exhibited a significant resistance to separate hot corrosion in liquid Al alloy and cavitation erosion phenomena in water. However, the combined effect of the two damaging mechanisms during ultrasound treatment of the molten alloy leaded to coating removal and to a horn consumption comparable to that of bare steel.
Abstract: Semisolid casting and non-dendritic solidification of commercially pure tin (about 1 °C freezing range) and Zamak 3 alloy (about 10 °C freezing range) by a modified serpentine channel method were studied. It was shown that semisolid casting of very small freezing range metals with a non-dendritic structure was possible using this method. The results showed that the wall of the copper serpentine channel mold acted as a substrate for heterogeneous copious nucleation of primary solid particles and the channel provided sufficient self-steering action to disperse the nuclei in the melt. The average diameter and shape factor of the primary particles in the semisolid cast CP-Sn sample was measured to be about 107 μm and 0.75, respectively. The average diameter and shape factor of the primary particles in the semisolid cast Zamak 3 alloy was measured to be about 16 μm and 0.8, respectively. Hardness of semisolid samples was slightly higher than those of conventional gravity cast samples.
Abstract: Semi-solid processing of Al-4.3%Cu (A206) alloy was performed by Gas Induced Semi-Solid (GISS) process in different condition. The flow rate of argon gas, starting temperature for gas purging (the temperature of superheated-melt) and the duration of gas purging were three key process variables which were changed during this investigation. It was found that inert gas purging near liquidus, significantly, led to the microstructural modification from fully dendritic to globular structure. Thermal analysis was successfully implemented through CA-CCTA technique to understand the cause of the microstructure change during GISS process. The results showed that gas purging into the melt leads to temperature drop of the melt to its liquidus just after a few seconds from start of gas purging. In fact, copious nucleation was induced by cooling effect of inert gas bubbles. Microstructural features were characterized in semi-solid as well as on conventionally cast samples. The optimum gas purging temperature, injection time, and inert gas flow rate was determined in semi-solid processing to obtain the best globularity in the microstructure of a long freezing range alloy. However, the microstructure of the conventionally cast sample was fully dendritic with shrinkage which affects the soundness of casting products.
Abstract: The application of the core-bar pulling method to Al-Mg, Al-Mn, Al-Cu and Cu-Zn alloys was investigated, using a stainless steel core-bar with a 2 mm diameter to produce through-holes in 50 mm long ingots. This study confirmed that through-holes could be produced in these alloys in this manner. The results demonstrate that the temperature ranges over which the core-bar can be extracted are quite wide, so precise control of the ingot temperature is not required when producing through-holes. The core-bar pulling method is evidently a facile means of fabricating through-hole lotus type porous metals.