高强韧铝合金AlSi10MnMg实现不同压铸力学性能的研究

根据AlSi10MnMg中不同Mg含量和不同热处理状态以及热处理工艺参数,通过对实验数据的分析研究,细分出不同状态下压铸力学性能的具体范围,以便根据不同应用场景的力学性能要求,选择相应的生产和热处理工艺。

Microstructures and properties of A356-10%SiC particle composite castings at different solidification pressures

A356-based metal matrix composites with 10% SiC particles of 10 rtm were fabricated by stir casting and direct squeeze casting process under applied pressures of 0.1 （gravity）, 25, 50 and 75 MPa. The microstructures and mechanical properties of the as-cast and T6 heat-treated castings were investigated. The results show that as the applied pressures increase, the casting defects as particle-porosity clusters reduce and the incorporation between the particles and matrix can be improved. The tensile strength, hardness, and coefficients of thermal expansion （CTE） increase with the increase of the pressures. Compared with the as-cast composite castings, the tensile strength and hardness of the heat-treated casting are improved whereas CTEs tend to decrease in T6-treated condition. For the gravity cast composites, there are some particle-porosity clusters on the fracture surface, and the clusters are hardly detected on the fracture surface of the samples solidified at the external pressures. Different fracture behaviors are found between the composites solidified at the gravity and imposed pressures.

Microstructure evolution and tensile mechanical properties of thixoformed AZ61 magnesium alloy prepared by squeeze casting

A novel process that combines squeeze casting with partial remelting to obtain AZ61 magnesium alloy with semi-solid microstructures was proposed. In this route, the squeeze casting was used to predeform the magnesium alloy billets to obtain small dendritic structures. During subsequent partial remelting, small dendritic structures transform into globular grains surrounded by liquid films. The results show that the squeeze casting AZ61 alloy after partial remelting produces more ideal, finer semi-solid microstructure compared with as-cast AZ61 alloy treated by the same isothermal holding conditions. Moreover, the mechanical properties of the thixoformed AZ61 alloy prepared by squeeze casting plus partial remelting are better than those of the thixoformed alloy prepared by conventional casting plus partial remelting.

Effect of applied pressure on microstructure and mechanical properties of Mg-Zn-Y quasicrystal-reinforced AZ91D magnesium matrix composites prepared by squeeze casting

The Mg-Zn-Y quasicrystal-reinforced AZ91 D magnesium matrix composites were prepared by squeeze casting process. The effects of applied pressure on microstructure and mechanical properties of the composites were investigated. The results show that squeeze casting process is an effective method to refine the grain. The composites are mainly composed of α-Mg, β-Mg17Al12 and Mg3Zn6Y icosahedral quasicrystal phase（I-phase）. With the increase of applied pressure, the contents of β-Mg17Al12 phase and Mg3Zn6 Y quasicrystal particles increase, further matrix grain refinement occurs and coarse dendritic α-Mg transforms into equiaxed grain structure. The composite exhibits the maximum ultimate tensile strength and elongation of 194.3 MPa and 9.2% respectively when the applied pressure is 100 MPa, and a lot of dimples appear on the tensile fractography. Strengthening mechanisms of quasicrystal-reinforced AZ91 D magnesium matrix composites are chiefly fine-grain strengthening and quasicrystal particles strengthening.

Mechanical properties and microstructures of Al alloy tensile samples produced by serpentine channel pouring rheo-diecasting process

An innovative one-step semi-solid processing technique of A356 Al alloy,the serpentine channel pouring rheo-diecasting process （SCRC）,was explored.The mechanical properties and microstructures of the tensile samples made by the SCRC technique were tested in the as-cast and T6 heat treatment conditions.The experimental results show that the as-cast ultimate tensile strength can reach about 250MPa and the elongation is 8.6%？13.2%.The ultimate tensile strength can increase approximately 30% higher than that of the as-cast one but there is some slight sacrifice of the plasticity after T6 heat treatment.Under these experimental conditions,the semi-solid A356 Al alloy slurry with primary α1（Al） grains,which have the shape factor of 0.78？0.89 and the grain diameter of 35？45μm,can be prepared by the serpentine channel pouring process.The primary α2（Al） grains are very fine during the secondary solidification stage.Compared with the conventional HPDC process,the SCRC process can improve the microstructures and mechanical properties of the tensile test samples.The advantages of the SCRC process include easily incorporating with an existing HPDC machine,cancelling the preservation and transportation process of the semi-solid alloy slurry,and a higher cost performance.

Low cycle fatigue behavior of T4-treated Al-Zn-Mg-Cu alloys prepared by squeeze casting and gravity die casting

Gravity die casting(GC) and squeeze casting(SC) T4-treated Al-7.0Zn-2.5Mg-2.1Cu alloys were employed to investigate the microstructures,mechanical properties and low cycle fatigue(LCF) behavior.The results show that mechanical properties of SC specimens are significantly better than those of GC specimens due to less cast defects and smaller secondary dendrite arm spacing(SDAS).Excellent fatigue properties are obtained for the SC alloy compared with the GC alloy.GC and SC alloys both exhibit cyclic stabilization at low total strain amplitudes(less than 0.4%) and cyclic hardening at higher total strain amplitudes.The degree of cyclic hardening of SC samples is greater than that of GC samples.Fatigue cracks of GC samples dominantly initiate from shrinkage porosities and are easy to propagate along them,while the crack initiation sites for SC samples are slip bands,eutectic phases and inclusions at or near the free surface.

Microstructure and mechanical properties of Mg-6Gd-3Y-0.5Zr alloy processed by high-vacuum die-casting

GW63K （Mg-6Gd-3Y-0.5Zr） magnesium alloys were prepared successfully by high-vacuum die-casting. Effects of fast shot speed and vacuum level on the grain size and mechanical properties of this alloy were studied. Microstructure of the alloys was analyzed by SEM, EDX and optical microscope （OM）. The effect of heat treatment on high vacuum die-casting （HVDC） GW63K alloy was also studied. The results indicate that with the increase of fast velocity, the tensile yield strength hardly changes, but the elongation first increases, then decreases. The optimum heat treatment process is solution treatment at 748 K for 2 h and aging at 473 K for 80 h. Under this condition, GW63K magnesium alloy exhibits a maximum tensile strength and elongation of 308 MPa and 9.45%. There is significant correlation between ductility and the presence of external solidified cells （ESCs）. The as-cast GW63K alloy consists ofα-Mg and Mg24（Gd,Y）5 particles. After heat treatment, Gd and Y atoms dissolve intoα-Mg matrix.

Microstructure evolution and mechanical properties of rheo-processed ADC12 alloy

Microstructure evolution and mechanical properties of the rheo-processed ADC12 alloy were investigated by means ofoptical microscopy, X-ray diffraction and scanning electron microscopy. Primary dendritic Al of rheo-casting (RC) andrheo-diecasting (RDC) ADC12 alloys are sheared off. The average size, as well as solid fraction of the primary Al increase withdescending pouring temperature. The mechanical properties of alloys are strengthened by rheo-processing. Ultimate tensile strengthsof RC samples increase with the decrease of the pouring temperature, and reach the maximum in the range from 580 to 600 °C. Atpouring temperature of 595 °C, the RDC sample obtains the best ultimate tensile strength and elongation. Great reductions onporosity and primary Al globularization are crucial to the mechanical properties. Relationships of the primary Al size and yield stressare depicted with Hall?Petch equation.

Influence of Ce addition on microstructure and mechanical properties of high pressure die cast AM50 magnesium alloy

The influence of Ce addition on the microstructure and mechanical properties of AM50 magnesium alloy was investigated to improve its mechanical properties.The results show that the addition of Ce to AM50 alloy results in the grain refinement and the mechanical properties of the Ce-modified AM50 at room and elevated temperatures are remarkably improved.AM50 magnesium alloy containing 1% Ce（mass fraction） shows better refinement and mechanical properties compared with the AM50 magnesium alloy with 0.5% Ce and even AM50 alloy without any Ce.

Microstructure,mechanical properties and corrosion behavior of Al-Si-Cu-Zn-X(X=Bi,Sb,Sr) die cast alloy

The microstructure evolution, mechanical and corrosion properties of Al-11Si-2Cu-0.8Zn die cast alloy treated with Bi, Sb and Sr additions were investigated. The results of mechanical testing showed that all additions increased impact toughness, ultimate tensile strength, and elongation of the alloy as a result of change in eutectic Si morphology. The analysis of fracture surfaces revealed that with addition of Sr and to lesser extent Bi and Sb, the alloy exhibited a predominantly ductile fracture rather than quasi-cleavage brittle fracture. Moreover, with the additions of Sr, Bi and Sb, the quality index increased to 164.7 MPa, 156.3 MPa and 152.6 MPa respectively from 102 MPa for the base alloy. Polarization corrosion tests conducted in sodium chloride solution showed that the corrosion potential shifted to more negative values with additions of Sb, Bi and Sr, respectively. Corrosion immersion tests also revealed that the element additions have a detrimental effect on the corrosion rate of alloys, due to the increase of boundaries between the Al and eutectic Si phases.

Influence of rheo-diecasting processing parameters on microstructure and mechanical properties of hypereutectic Al-30%Si alloy

The effects of pouring temperature,vibration frequency,and the number of curves in a serpentine channel,on themicrostructure and mechanical properties of Al-30%Si alloy processed by rheo-diecasting(RDC)were investigated.The semisolidAl-30%Si alloy slurry was prepared by vibration serpentine channel pouring(VSCP)process in the RDC process.The results showthat the pouring temperature,the vibration frequency,and the number of the curves strongly affect the microstructure and mechanicalproperties of Al-30%Si alloy.Under experimental conditions of a pouring temperature of850°C,a twelve-curve copper channel anda vibration frequency of80Hz,the primary Si grains are refined into fine compact grains with average grain size of about24.6μm inthe RDC samples assisted with VSCP.Moreover,the ultimate tensile strength(UTS),elongation and hardness of the RDC sample are296MPa,0.87%and HB155,respectively.It is concluded that the VSCP process can effectively refine the primary Si grains.Therefinement of primary Si grains is the major cause for the improvement of the mechanical properties of the RDC sample.

Effects of combined addition of Y and Ca on microstructure and mechanical properties of die casting AZ91 alloy

A series of die casting heat-resistant magnesium alloys based on Mg-Al system were developed for automotive application by adding Y and various amounts of Ca. The mechanical properties and microstructures of die casting AZ91 alloy with combined addition of Y and Ca were investigated by optical microscopy, scanning electronic microscopy, X-ray diffractometry and mechanical property test. The results show that the combined addition of Y and Ca can refine the as-die-cast microstructure, result in the formation of Al2Ca phase and Al2Y phase, and inhibit the precipitation of Mg17Al12 phase. The combined addition of Y and small amount of Ca has little influence on the ambient temperature tensile properties, but increasing the content of Ca can improve significantly the tensile strength at both ambient and elevated temperatures. It is found that for AZ91-1Y-xCa alloy, the hardness and the elevated temperature tensile strength increase, while the elongation decreases with increasing the addition of Ca. The mechanism of mechanical properties improvement caused by the combined addition of Y and Ca was also discussed.

Microstructure evolution of modified die-cast AlSi10MnMg alloy during solution treatment and its effect on mechanical properties

To optimize the solution treatment process of a modified high-pressure die-cast AlSi10MnMg alloy, the influence of the solution treatment on the microstructure, mechanical properties and fracture mechanisms was studied using OM, SEM, EBSD and tensile test. The experimental results suggest that the solution treatment could be completed in a shorter time at a temperature much lower than the conventional practice. Surface blistering could be avoided and substantial strengthening effect could be achieved in the following aging process. Prolonging solution treatment time and elevating solution temperature would be meaningless or even harmful. The rapid evolution of eutectic silicon during solution treatment, especially at the early stage, affected the way of interaction among α-Al grains during plastic deformation, and changed the ultimate mechanical properties and fracture mode.

Microstructure and mechanical properties of die-cast AZ91D magnesium alloy by Pr additions

Mg-9Al-xPr(x=0.4,0.8 and 1.2,mass fraction,%)magnesium alloys were prepared by high-pressure die-casting technique.The effects of Pr on the microstructures of die-cast Mg-9Al based alloy were investigated by XRD and SEM.Needle-like Al11Pr3 phase and polygon Al6Mn6Pr phase are found in the microstructure.With 0.4%Pr addition,fine needle-like Al11Pr3 phase and a small amount of polygon Al6Mn6Pr phase near the grain boundary are found in the microstructure.Increasing Pr addition to 0.8%, lots of coarse needle-like Al11Pr3 phase within grain and polygon Al6Mn6Pr phase on grain boundary are observed.Further increasing Pr addition,the size of needle-like Al11Pr3 phase decreases,while the size of polygon Al6Mn6Pr relatively increases.The mass fraction of Pr at around 0.8%is considered to be suitable to obtain the optimal mechanical properties.The optimal mechanical properties are mainly resulted from grain boundary strengthening obtained by precipitates and solid solution.

Microstructure and mechanical properties of extruded Al/Al_2O_3 composites fabricated by stir-casting process

A novel two step mixing method including injection of particles into the melt by inert gas and stirring was used to prepare aluminum matrix composites （AMCs） reinforced with Al2O3 particles. Different mass fractions of micro alumina particles were injected into the melt under stirring speed of 300 r/min. Then the samples were extruded with ratios of 1.77 or 1.56. The microstructure observation showed that application of the injection and extrusion processes led to a uniform distribution of particles in the matrix. The density measurements showed that the porosity in the composites increased with increasing the mass fraction of Al2O3 and stirring speed and decreased by extrusion process. Hardness, yield and ultimate tensile strengths of the extruded composites increased with increasing the particle mass fraction to 7%, while for the composites without extrusion they increased with particle mass fraction to 5%.

Microstructure and mechanical properties of melt-conditioned high-pressure die-cast Mg-Al-Ca alloy

A new shape casting process,melt-conditioned high-pressure die-casting(MC-HPDC) was developed.In this process,liquid metal was conditioned under intensively forced convection provided by melt conditioning with advanced shear technology(MCAST) unit before being transferred to a conventional cold chamber high-pressure die-casting(HPDC) machine for shape casting. The effect of melt conditioning was investigated,which was carried out both above and below the liquidus of the alloy,on the microstructure and properties of a Mg-Al-Ca alloy(AZ91D+2%Ca(mass fraction) ,named as AZX912) .The results show that many coarse externally-solidified crystals(ESCs) can be observed in the centre of conventional HPDC samples,and hot tearing occurs at the inter-dendritic region because of the lack of feeding.With the melting conditioning,the MC-HPDC samples not only have considerably refined size of ESCs but also have significantly reduced cast defects,thus provide superior mechanical properties to conventional HPDC castings.The solidification behaviour of the alloy under different processing routes was also discussed.

Microstructure and mechanical properties of extruded Mg-6.5Gd-1.3Nd-0.7Y-0.3Zn alloy

The Mg-6.5Gd-1.3Nd-0.7Y-0.3Zn alloy ingot and sheet were prepared by casting and hot extrusion techniques,and the microstructure,age hardening behavior and mechanical properties were investigated.The results show that the as-cast alloy mainly containsα-Mg solid solution and compounds of Mg5RE and Mg24RE5(RE=Gd,Y and Nd)phases.The grain size is refined after hot extrusion,and the Mg5RE and Mg24RE5 compounds are broken during the extrusion process.The extruded alloy exhibits remarkable age hardening response and excellent mechanical properties in the peak-aging state.The ultimate tensile strength,yield strength and elongation are 310 MPa,201 MPa and 5.8%at room temperature,and 173 MPa,133 MPa and 25.0%at 300℃,respectively.