Microstructures in Centrifugal Casting of SiC_p/AlSi9Mg Composites with Different Mould Rotation Speeds

Two ingots were produced by centrifugal casting at mould rotational speeds of 600 rpm and 800 rpm using 20 vol%SiC p /AlSi9Mg composite melt,respectively.The microstructure along the radial direction of cross-sectional sample of ingots was presented.SiC particles migrated towards the external circumference of the tube,and the distribution of SiC particles became uniform under centrifugal force.Voids in 20 vol%SiC p /AlSi9Mg composite melt migrated towards the inner circumference of the tube.The quantitative analysis results indicated that not only SiC particles but also primaryαphases segregated greatly in centrifugal casting resulting from the transportation behavior of constitutions with different densities in the SiC p /AlSi9Mg composite melt.In addition,the eutectic Si was broken owing to the motion of SiC p /AlSi9Mg composite melt during centrifugal casting.

Microstructures and corrosion behaviors of Al−6.5Si−0.45Mg−xSc casting alloy

The microstructures and corrosion behaviors of the Al−6.5Si−0.45Mg casting alloys with the addition of Sc were investigated by using scanning electron microscopy,X-ray diffraction,electrochemical measurement techniques and immersion corrosion tests and compared with those of Sr-modified alloy.The results show that Sc has evident refining and modifying effects on the primaryα(Al)and the eutectic Si phase of the alloy,and the effects can be enhanced with the increase of Sc content.When the Sc content is increased to 0.58 wt.%,its modifying effect on the eutectic Si is almost same as that of Sr.Sc can improve the corrosion resistance of the test alloy in NaCl solution when compared with Sr,but the excessively high Sc content cannot further increase the corrosion resistance of the alloy.The corrosion of the alloys mainly occurs in the eutectic region of the alloy,and mostly the eutecticα(Al)is dissolved.This confirms that Si phase is more noble thanα(Al)phase,and the galvanic couplings can be formed between the eutectic Si andα(Al)phases.

Tape Casting of Al_2O_3-TiB_2/Al_2O_3-Nano-TiC Multilayer Composites

Ceramic tapes, containing Al2O3-25 wt pct TiB2(B) and Al2O3-25 wt pct nano-TiC (c), have been obtained by tape casting process. Numerous tapes (about 60～80 tapes) were prepared by stacking in turn the composition (B) and (C), laminating under 10 MPa pressure, eliminating the solvent and burning out the polymer additives. The final green bodies were hot pressed at 1750℃ and 30 MPa. The composite has a bending strength of 568 MPa and a fracture toughness of 5.8 M Pa·m1/2. SEM analysis exhibits that Al2O3 particle growth was inhibited by TiC particles in C. but TiB2 particles could not hinder Al2O3 growth in B. The curves of GTA indicates that all organic additives could be removed completely above 600℃

Finite element simulation of real cavity closure in cast Ti6Al4V alloy during hot isostatic pressing

The healing behavior of shrinkage cavity inside the cast Ti6Al4V alloy during hot isostatic pressing(HIP)was investigated experimentally by interrupted hot isostatic pressing tests.The X-ray micro computed tomography was used to record the morphology changes before and after hot isostatic pressing.The two-dimensional geometry obtained by the microCT scan was used in simulation to study the evolution of the real shrinkage cavity during hot isostatic pressing.Shrinkage cavities,shrinkage porosity and small gas pores can be effectively eliminated under proper HIP conditions.The two-dimensional morphology in the simulation results agrees well with the experimental results.This study reveals that plastic deformation,creep and diffusion are the main mechanisms of cavity closure during hot isostatic pressing.In addition,the simplified elliptical pores with aspect ratios at different positions were used to replace the real pores to further study the factors affecting the position of dimples after HIP by simulation.It is found that the position of the dimples mainly depends on the aspect ratio of the elliptical pore and the distance between the pore surface and the external surface of the geometric model.

Effect of Aging Treatment on Microstructural and Mechanical Characteristics of PEO Coatings on Mg-Al Alloy

Cast Mg-6 wt pct Al alloy solution-treated at 683 K for 16 h and aged at 498 K was coated by plasma electrolytic oxidation （PEO） method.The Mg-6 wt pct Al alloy aged for 16 h exhibited the highest microhardness and wear resistance.After PEO coating,however,the microhardness and wear resistance of coatings on Mg- 6 wt pct Al alloy showed a tendency to decrease with increasing aging time,which was in aggrement with the change of thickness with aging time.In addition,the coatings on solution-treated Mg-6 wt pct Al alloy had better microhardness and wear resistance than those on aged Mg-6 wt pct Al alloys.Consequently,it can be understood that the aging treatment has a deleterious influence on the mechanical properties of coatings on Mg-6 wt pct Al alloy.

Effect of Cu addition on overaging behaviour,room and high temperature tensile and fatigue properties of A357 alloy

The aims of the present work are to evaluate the overaging behaviour of the investigated Cu-enriched alloy and to assess its mechanical behaviour,in terms of the tensile and fatigue strength,at room temperature and at 200℃,and to correlate the mechanical performance with its microstructure,in particular with the secondary dendrite arm spacing(SDAS).The mechanical tests carried out on the overaged alloy at 200℃ indicate that the addition of about 1.3 wt.%Cu to the A357 alloy enables to maintain ultimate tensile strength and yield strength values close to 210 and 200 MPa,respectively,and fatigue strength at about 100 MPa.Compared to the quaternary(Al−Si−Cu−Mg)alloy C355,the A357−Cu alloy has greater mechanical properties at room temperature and comparable mechanical behaviour in the overaged condition at 200℃.The microstructural analyses highlight that SDAS affects the mechanical behaviour of the peak-aged A357−Cu alloy at room temperature,while its influence is negligible on the tensile and fatigue properties of the overaged alloy at 200℃.

THE CORROSION OF Al CAST IRON IN Zn LIQUID BATH

When cast iron is added with Al, the compound layer formed by reaction between cast iron and liquid Zn at 500～600℃ consists of nubby δ +Fe-Al phases instead of column δ+г phases, and the width of the compound layer increases obviously. The consumption of Fe in cast iron is dominated by the diffusive rate of Fe through the compound layer, therefore, the corrosive rate of cast iron is decreased remarkably. With increasing the content of Al in cast iron, the corrosive rate of the cast iron further decrease. For the cast iron containing 8.1 wt.% Al, its corrosive rate is ten times as low as that of general gray cast iron.

STATISTICAL MODEL FOR FRACTURE TOUGHNESS OF A MODIFIED Al-7Si-0.45Mg CAST ALLOY

The statistical model for the fracture toughness of a modified Al-7Si-0.45Mg cast alloy has been proposed on the basis of analysis of the correlation between the size distribution of crack nuclei and Si particles and of the micromechanism of fracture.The suitable criterion of frac- ture toughness according to the model has been given.The model has found a good explana- tion for the fracture feature,fracture toughness and microstructure,and agreed with the ex- periments very well.

Effects of Mg Enhancement and Heat Treatment on Microstructures and Tensile Properties of Al2Ca-Added ADC12 Die Casting Alloys

The effects of Mg enhancement and heat treatment on the microstructures and tensile properties of Al_2Ca-added ADC12 die casting alloys were investigated. 0.3% and 0.5% Mg in the form of a master alloy including a trace amount of Al_2Ca were added to conventional ADC12（383 and AlSi10Cu2Fe） alloy with an initial Mg-content of 0.3% to increase the Mg content to 0.6% and 0.8%, respectively. To avoid heat treatmentinduced surface blisters, shortened solution treatment for 15 min at 490 ℃ and artificial aging for 6 h at 150 ℃ was undertaken. The results show that a 10% improvement in the shape factor of eutectic Si particles was achieved for Al_2Ca-added ADC12 with 0.8% Mg compared to the conventional ADC12 in the as-aged condition. Al_2Ca-added ADC12 with 0.8% Mg exhibited a yield strength of 289 MPa, a tensile strength of 407 MPa, and an elongation of 4.22%.

Effect of Different Ageing Processes on Microstructure and Mechanical Properties of Cast Al–3Li–2Cu–0.2Zr Alloy

The effect of different ageing processes on microstructure and mechanical properties of cast Al–3 Li–2 Cu–0.2 Zr alloy was investigated using transmission electron microscopy and tensile tests. The results showed that the mean size of δ′-Al3 Li particles and the number density of Cu-rich precipitates both increased with increasing ageing temperature from 150 to 190 °C for 24 h, resulting in increasingly high strength. In contrast, the ductility deteriorated with the increase in ageing temperature as a result of the intensified planar slip. The duplex low-to-high ageing treatment(120 °C for 6 h followed by 160 °C for 24 h) was shown to be beneficial to the ductility compared with the corresponding single-stage ageing treatment(160 °C for 24 h). The reduced slip length induced by the precipitation of θ′-Al 2 Cu phases was found to be mainly responsible for this ductility improvement.

Effects of Solution Treatment on the Microstructure,Tensile Properties,and Impact Toughness of an Al–5.0Mg–3.0Zn–1.0Cu Cast Alloy

This study investigates the eff ect of solution treatment(at 470°C for 0–48 h)on the microstructural evolution,tensile properties,and impact properties of an Al–5.0Mg–3.0Zn–1.0Cu(wt%)alloy prepared by permanent gravity casting.The results show that the as-cast microstructure consists ofα-Al dendrites and a network-like pattern of T-Mg32(AlZnCu)49 phases.Most of the T-phases were dissolved within 24 h at 470℃;and a further prolonging of solution time resulted in a rapid growth ofα-Al grains.No transformation from the T-phase to the S-Al2CuMg phase was discovered in this alloy.Both the tensile properties and impact toughness increased quickly,reached a maximum peak value,and decreased gradually as the solution treatment proceeded.The impact toughness is more closely related to the elongation,and the relationship between impact toughness and elongation appears to obey an equation:IT=8.43 EL-3.46.After optimal solution treatment at 470℃for 24 h,this alloy exhibits excellent mechanical properties with the ultimate tensile strength,yield strength,elongation and impact toughness being 431.6 MPa,270.1 MPa,19.4%and 154.7 kJ/m^(2),which are comparable to that of a wrought Al–6.0 Mg–0.7 Mn alloy(5E06,a 5 xxx aluminum alloy).Due to its excellent comprehensive combination of mechanical properties,this cast alloy has high potential for use in components which require medium strength,high ductility and high toughness.