Synchronously Improving the Thermal Conductivity and Mechanical Properties of Al-Si-Fe-Mg-Cu-Zn Alloy Die Castings Through Ultrasonic-Assisted Rheoforming

An ultrasonic vibration-assisted air-cooled stirring rod process (ACSR + UV) was used to efficiently prepare a large-volume semisolid slurry with a mass of more than 40 kg.A low-cost Al-Si-Fe-Mg-Cu-Zn die-casted alloy with high thermal conductivity,high plasticity and medium strength was developed.The alloy was used to manufacture large,thin-walled parts for 5G base stations by using the ACSR + UV rheological die-casting (ACSR + UV R-DC) process.Investigations were performed on the microstructure,porosity,mechanical properties,fracture behaviour and thermal conductivity of the ACSR + UV R-DC alloy,which was then compared to traditionally die-casted (T-DC) and ACSR R-DC alloys.The mecha-nisms for the microstructural refinement and enhancement of the mechanical and thermal conductivity performances of the ACSR + UV R-DC alloy were also analysed.The results showed that the ACSR + UV process increased the nucleation rate of the melt due to the increase in the nucleation area and the generation of cavitation bubbles.A radial-and an axial-forced convection was also generated inside the melt under the combined effects of acoustic flow and mechanical stirring,thereby homogenising the melt composition field and the temperature field.Therefore,the ACSR + UV R-DC process not only refined the primary α-Al (α1-Al),the eutectic silicon and the secondary α-Al (α2-Al),but also greatly improved the mor-phology and the distribution of the β-Al5FeSi phase.The mechanical properties of the ACSR + UV R-DC alloy were higher than those of the T-DC and the ACSR R-DC alloys.Compared to the T-DC alloy,the ultimate tensile strength,elongation and yield strength of the ACSR + UV R-DC alloy were increased by 34％,122％ and 19％,respectively.This was because the ACSR + UV R-DC technique gave the alloy the characteristics of high density,fine spherical α1-Al grain and a fine and uniform β-phase,which improved the fracture behaviour of the alloy.The thermal conductivity of the ACSR + UV R-DC alloy was 184 W/(m K),which was 10.2％ and 3.4％ higher than that of T-DC and ACSR R-DC alloys,respectively.This was because the refined eutectic silicon and β phases in the ACSR + UV R-DC alloy facilitated an easier electron flow through the eutectic region,and the decrease in porosity increased the effective area of heat conduction.     

The indirect ultrasonic vibration process for rheo-squeeze casting of A356 aluminum alloy

The semisolid slurry of A356 Al alloy was prepared by indirect ultrasonic vibration (IUV) method and then formed by direct squeeze casting (SC). The effects of squeeze pressure and T6 heat treatment on the microstructure and mechanical properties of rheo-squeeze casting (RSC) A356 Al alloy were investigated. The results indicate that with the increase of squeeze pressure, the average diameter of primary α-Al particles decreased, while the densities and mechanical properties of the samples increased. The effect of T6 heat treatment on the mechanical properties is more significant in RSC samples than in conventional SC samples. The tensile strength and elongation of T6 heat treated RSC samples under 100 MPa pressure are 338 MPa and 8%, respectively.     

Effects of melt treatment temperature and isothermal holding parameter on water-quenched microstructures of A356 aluminum alloy semisolid slurry

The semisolid slurry of the A356 aluminum alloy was prepared by self-inoculation method (SIM), the effects of melt treatment temperatures and isothermal holding parameters on water-quenched microstructures of A356 aluminum alloy semisolid slurry were investigated, and the solidification behavior of the remaining liquid phase (secondary solidification) was analyzed. The results indicate that the melt treatment temperature has significant effects on the final semisolid microstructures. The semisolid slurry which is suitable for the rheological forming can be produced when the melt treatment temperature is between 680 and 690 °C. During the isothermal holding process, the growth rate of the primary particles conforms to the dynamic equation of D_t³–D₀³=Kt, and the coarsening rate of the primary particles is the fastest when the isothermal holding temperature is 600 °C. Additionally, the isothermal holding time also has obvious effect on the secondary solidification microstructures. The secondary particles are the smallest and roundest when the isothermal holding time is 3 min. The amount of the secondary particles gradually increases with the increase of isothermal holding temperature, and the eutectic reaction therefore is confined into small intergranular areas, contributing to the compactness of the final solidified eutectic structures.     

流变模锻A356铝合金的显微组织和力学性能

采用机械搅拌法制备A356合金半固态浆料,在200 t油压机上进行流变模锻成形,研究了流变模锻试样热处理前后的组织和力学性能.结果表明:流变模锻试样组织由球形α-Al晶粒和α+Si共晶组织组成;热处理前试样抗拉强度为261.7 MPa,伸长率为4.1％;经T6热处理后,试样抗拉强度为347.8 MPa,提高了32.9％...     

Solidification behavior and rheo-diecasting microstructure of A356 aluminum alloy prepared by self-inoculation method

Semisolid slurry of A356 aluminum alloy was prepared by self-inoculation method, and the microstructure and solidification behavior during rheo-diecasting process were investigated. The results indicate that the semisolid slurry of A356 aluminum alloy can be prepared by self-inoculation method at 600 °C. Primary α-Al particles with fine and spherical morphologies are uniformly distributed when the isothermal holding time of slurry is 3 min. Liquid phase segregation occurs during rheo-diecasting process of semisolid slurry and the primary particles(α1) show obvious plastic deformation in the area of high stress and low cooling rate. A small amount of dendrites resulting from the relatively low temperature of the shot chamber at the initial stage of secondary solidification are fragmented as they pass through the in-gate during the mould filling process. The amount of dendrite fragments decreases with the increase of filling distance. During the solidification process of the remaining liquid, the nucleation rate of secondary particles(α2) increases with the increase of cooling rate, and the content of Si in secondary particles(α2) are larger than primary particles(α1). With the increase of cooling rate, the content of Si in secondary particles(α2) gradually increases. The morphologies of eutectic Si in different parts of die casting are noticeably different. The low cooling rate in the first filling positions leads to coarse eutectic structures, while the high cooling rate in the post filling positions promotes small and compact eutectic structures.     

Solidification behavior of 6061 wrought aluminum alloy during rheo-diecasting process with self-inoculation method

The semisolid slurry of the 6061 wrought aluminum alloy was prepared by the self-inoculation method (SIM). The effects of the isothermal holding parameters on microstructures of rheo-diecastings were investigated, and the solidification behavior of 6061 wrought aluminum alloy during the rheo-diecasting process was analyzed using OM, SEM, EDS and EBSD. The results indicate that the isothermal holding process during slurry preparation has great effect on primary α(Al) particles (α₁), but has little effect on the microstructure of secondary solidification in the process of thin-walled rheo-diecasting. Nucleation is expected to take place in the entire remaining liquid when the remaining liquid fills the die cavity, and the secondary solidification particles (α₂) are formed after the process of stable growth, unstable growth and merging. The solute concentration of remaining liquid is higher than that of the original alloy due to the existence of α₁ particles, hence the contents of Mg and Si in α₂ particles are higher than those in α₁ particles.     

Rheo-squeeze casting of semi-solid A356 aluminum alloy slurry

The effect of pouring temperature, electromagnetic stirring power and holding process on semi-solid A356 aluminum alloy slurry was investigated, then the slurry was squeeze-cast. The results show that when the pouring temperatures are properly above the liquidus line, for example 630-650 °C, the slurry with spherical primary α(Al) grains can be prepared under the stirring power of 1.27 kW. The slurry is then homogeneously held for a short time, and the primary α(Al) grains are further ripened and distributed evenly in the slurry. The results of the rheo-squeezed casting experiments show that the injection specific pressure has a great effect on the filling ability of the semi-solid A356 aluminum alloy slurry, and the higher the injection specific pressure is, the better the ability for the slurry to fill the mould cavity is. When the injection specific pressure is equal to or above 34 MPa, the whole and compact rheo-squeezed castings can be obtained. The microstructure of the castings indicates that the shape, size and numbers of the primary α(Al) grains in different parts of the castings are highly consistent. After being held at 535 °C for 5 h and then aged at 155 °C for 12 h, the ultimate strength of the rheo-squeezed castings can reach 300-320 MPa, the yield strength 230-255 MPa, and the elongation 11%-15%.     

Preparation of Al-Zn-Mg-Cu alloy semisolid slurry through a water-cooled serpentine pouring channel

The semisolid slurry of Al-Zn-Mg-Cu alloy was prepared through a self-designed water-cooled copper serpentine pouring channel(WSPC) machine. Influences of pouring temperature, the number of turns and the cooling water flow rate on the microstructure of the semisolid Al-Zn-Mg-Cu alloy slurry were investigated. The results show that the semisolid Al-Zn-Mg-Cu alloy slurry with satisfactory quality can be generated by the WSPC when the pouring temperature is in the range between 680 ℃ and 700 ℃. At a given pouring temperature, the average grain size of primary α-Al decreases and the shape factor increases with the increase of the number of turns. When the cooling water flow rate is 450 L·h~(-1), the obtained semisolid slurry is optimal. During the preparation of the semisolid Al-Zn-Mg-Cu alloy slurry with low superheat pouring, the alloy melt has mixed inhibition and convection flow characteristics by "self-stirring". When the alloy melt flows through the serpentine channel, the chilling effect of the inner wall of the channel, the convection and mixed inhibition of the alloy melt greatly promote the heterogeneous nucleation and grain segregation. This effect destroys the dendrite growth mode under traditional solidification conditions, and the primary nuclei gradually evolve into spherical or nearspherical grains.     

Effect of yttrium on the microstructure of a semi-solid A356 Al alloy

The semi-solid slurry of an A356 Al alloy,which was grain-freed by yttrium,was manufactured by low temperature pouring.The effects of grain-refining on the morphology and the grain size of the primary α phase in the semi-solid A356 Al alloy were researched.The results indicate that the semi-solid A356 Al alloy with particle-like and rosette-like primary α-Al can be prepared by low temperature pouring from a liquid grain-refined A356 alloy.The grain size and particle morphology of primary α-Al in the A356 Al alloy are markedly improved by the addition of 0.5 wt.% Y.The fining mechanism of Y on the morphology and grain size of the primary α-Al in the semi-solid A356 Al alloy was delved.     

Microstructure and properties of rheo-HPDC Al-8Si alloy prepared by air-cooled stirring rod process

A new and effective semisolid slurry preparation process with air-cooled stirring rod (ACSR) is reported, in which the compressed air is constantly injected into the inner cavity of a stirring rod to cool the melt. The slurry of a newly developed high thermal conductivity Al-8Si alloy was prepared, and thin-wall heat dissipation shells were produced by the ACSR process combined with a HPDC machine. The effects of the air flow on the morphology of α₁-Al particles, mechanical properties and thermal conductivity of rheo-HPDC samples were studied. The results show that the excellent slurry of the alloy could be obtained with the air flow exceeding 3 L/s. Rheo-HPDC samples that were produced with the air flow of 5 L/s had the maximum UTS, YS, elongation, hardness and thermal conductivity of 261 MPa, 124 MPa, 4.9%, HV 99 and 153 W/(m·K), respectively. Rheo-HPDC samples show improved properties compared to those formed by HPDC, and the increasing rates of UTS, YS, elongation, hardness and thermal conductivity were 20%, 15%, 88%, 13% and 10%, respectively.     

新型高强度压铸Al-Si-Mg-Mn合金组织和性能的演变

研究了新型高强度Al-Si-Mg-Mn合金组织和性能的演变.基于JMatPro相图模拟计算,设计了不同共晶体积分数的Al-Si-Mg-Mn合金成分.结果 表明,新型Al-Si-Mg-Mn合金压铸后(铸态)的抗拉强度可达230～310MPa,屈服强度200～240MPa,伸长率约0.5％.铸态组织中包含α-Al、α-Al...     

Determining effect of slurry process parameters on semisolid A356 alloy microstructures produced by RheoMetal process

Abstract

The RheoMetal process, based on the rapid slurry forming (RSF) technology, is a new rheocasting process enabling the production of semisolid slurry of high quality and with high efficiency. The RSF technology is based on an enthalpy exchange between two alloy systems rather than applying external cooling as is done in many other rheocasting processes. In this work, several process parameters important for the RSF technology have been investigated on aluminium A356 alloy slurry microstructures. During slurry preparation, the thermal history for the different parameters studied was also recorded. It was found that the process parameters tested (amount of solid addition, melt superheat, rotation speed) have an effect on the thermal history during processing and on the microstructures formed after slurry formation.     

熔体浇注温度和板倾斜度对倾斜板制备A356铝合金的凝固和显微组织的影响(英文)

采用倾斜板制备A356铝合金半固态浆料。通过倾斜板底部的逆流水冷却使A356合金熔体在流下倾斜板时发生局部凝固,从而导致在板壁上形成连续柱状枝晶。由于强制对流作用,这些树枝晶被折断成等轴和破碎的晶粒,然后被连续冲洗而在斜板出口形成半固态浆料。熔体浇注温度是影响凝固组织的重要条件,而倾斜度为优质半固态浆料提供必要的剪切作用。将得到的浆料在金属模具中凝固以制备理想显微组织的半固态铸造坯料。然后,通过热处理以提高半固态铸造坯料的表面质量。对半固态铸造和热处理后坯料的显微组织进行分析。研究熔体浇注温度(620,625,630和635°C)和板倾斜度(30°,45°,60°和75°)对斜板制备A356铝合金的凝固和显微组织的影响。结果表明:在625°C的熔体浇注温度和60°斜板倾角时,A356铝合金具有细小和球状的晶粒,是最佳的显微组织。     

Influence of temper condition on microstructure and mechanical properties of semisolid metal processed Al–Si–Mg alloy A356

Abstract

The microstructures and mechanical properties of strontium modified semisolid metal high pressure die cast A356 alloy are presented. The alloy A356-F (as cast) has a globular primary grain structure containing a fine eutectic. Solution treatment results in spheroidisation of the eutectic silicon particles under the T4 and T6 temper conditions. The A356-T5 maintains the fibrous silicon morphology after artificial aging. A356-T4 has better ductility and impact strength than A356-T5 due to its spheroidised silicon morphology. The impact properties of semisolid metal high pressure die cast A356 are controlled mainly by the silicon morphology and alloy strength (hardness), whereas tensile strength is determined by the degree of solid solution coupled with precipitate formation during aging.     

Effects of nano-SiCp content on microstructure and mechanical properties of SiCp/A356 composites assisted with ultrasonic treatment

nano-SiC_p/A356 composites with different nano-SiC_p contents were prepared by squeeze casting after ultrasonic treatment (UT). The effects of SiC_p content on the microstructure and mechanical properties of the nanocomposites were investigated. The results show that with the addition of nano-SiC_p, the microstructure of nanocomposites is obviously refined, the morphology of the α(Al) grains transforms from coarse dendrites to rosette crystals, and long acicular eutectic Si phases are shortened and rounded. The mechanical properties of 0.5%, 1% and 2% (mass fraction) SiC_p/A356 nanocomposites are improved continuously with the increase of nano-SiC_p content. Especially, when the SiC_p content is 2%, the tensile strength, yield strength and elongation are 259 MPa, 144 MPa and 5.3%, which are increased by 19%, 69% and 15%, respectively, compared with those of the matrix alloy. The improvement of strength is attributed to mechanisms of Hall-Petch strengthening and Orowan strengthening.     

A356铝合金Al-5Ti-1B和Al-10Sr熔体处理遗传效应

通过重熔试验研究Al-5Ti-1B和Al-10Sr中间合金在A356熔体中的遗传效应。结果表明:A356合金经熔体处理后流动性较母材提高17.36%,T6处理后α-Al枝晶细化,二次枝晶间距仅为16.8μm,共晶硅圆整,抗拉强度达269 MPa、屈服强度203MPa、伸长率12.5%、硬度92 HBW。伴随重熔,细化变质效果逐渐衰退,熔体质量下降,以致力学性能和流动性下降。试验发现固溶后快淬可减小变质衰退带来的影响。     

Effect of heat treatment on microstructures and mechanical properties of A356 alloy cast through rapid slurry formation (RSF) process

The effect of T5 heat treatment on microstructure and mechanical properties of A356 alloy was observed. The as-cast A356 alloy exhibited coarse dendrites and long Si needles. RSF process changed the dendritic α-Al phase to globular morphology which helps in improving the mechanical properties of the alloy. The addition of 0.6wt-% Al–5Ti–1B grain refiner refined the average grain size of primary α-Al phase. T5 heat treatment at 170 °C for 20 h in different processing conditions was given to A356 alloy. T5 heat treatment led to further refinement of α-Al phase and Si needles, precipitation hardening due to Mg₂Si phase and reduction in the porosity level (%). The Quality Index for A356 alloy in different processing conditions was also measured. Results showed that RSF process with the use of baffles, addition of grain refiner and T5 heat treatment had improved the mechanical properties over other processing conditions.     

Effect of pouring temperature on fractal dimension of primary phase morphology in semi-solid A356 alloy

The fractal dimensions of primary phase morphology in semi-solid A356 alloy prepared by low superheat pouring and slightly electromagnetic stirring were calculated, and the effect of pouring temperature on fractal dimension of primary phase morphology in semi-solid A356 alloy was researched. The results indicate that it is feasible to prepare semisolid A356 alloy slurry by low superheat pouring and slightly electromagnetic stirring, and there is an important effect of pouring temperature on the morphology and the grain size of the primary phase in semi-solid A356 alloy, in which the reduction of pouring temperature can obviously improve grain size and shape factor of primary phase in semi-solid A356 alloy under the condition of a certain stirring power. The primary phase morphology of semi-solid A356 alloy prepared by low superheat pouring and slightly electromagnetic stirring can be characterized by fractal dimension, and the primary phase morphology obtained by the different processing parameters has the different fractal dimensions. Solidification of semi-solid alloy is a course of change in fractal dimension.     

Semisolid slurry of 7A04 aluminum alloy prepared by electromagnetic stirring and Sc,Zr additions

Slurry preparation is one of the most critical steps for semisolid casting, and its primary goal is to prepare slurry with uniformly distributed fine globules. In this work, electromagnetic stirring(EMS) and the addition of Sc and Zr elements were used to prepare semisolid slurry of 7A04 aluminum alloy in a large diameter slurry maker. The effects of different treatments on the microstructure, composition and their radial homogeneity were investigated. The results show that, compared to the slurry without any treatment, large volume slurry with finer and more uniform microstructure can be obtained when treated by EMS, Sc, or Zr additions individually. EMS is more competent in the microstructural and chemical homogenization of the slurry while Sc and Zr additions are more excellent in its microstructural refinement. The combined treatment of EMS, Sc and Zr produces premium 7A04 aluminum alloy slurry with uniformly distributed fine α-Al globules and composition. The interaction mechanism between EMS and Sc and Zr additions was also discussed.     

Ultrasonic Vibration and Rheocasting for Refinement of Mg–Zn–Y Alloy Reinforced with LPSO Structure

In this work, ultrasonic vibration (UV) and rheo-squeeze casting was first applied on the Mg alloy reinforced with long period stacking ordered (LPSO) structure. The semisolid slurry of Mg–Zn–Y alloy was prepared by UV and processed by rheo-squeeze casting in succession. The effects of UV, Zr addition and squeeze pressure on microstructure of semisolid Mg–Zn–Y alloy were studied. The results revealed that the synergic effect of UV and Zr addition generated a finer microstructure than either one alone when preparing the slurries. Rheo-squeeze casting could significantly refine the LPSO structure and α-Mg matrix in Mg_96.9Zn₁Y₂Zr_0.1 alloy without changing the phase compositions or the type of LPSO structure. When the squeeze pressure increased from 0 to 400 MPa, the block LPSO structure was completely eliminated and the average thickness of LPSO structure decreased from 9.8 to 4.3 μm. Under 400 MPa squeeze pressure, the tensile strength and elongation of the rheocast Mg_96.9Zn₁Y₂Zr_0.1 alloy reached the maximum values, which were 234 MPa and 17.6%, respectively, due to its fine α-Mg matrix (α1-Mg and α2-Mg grains) and LPSO structure.