The aluminum–silicon eutectic reaction: mechanisms and crystallography

Effect of high-intensity ultrasonic irradiation on the modification of solidification microstructure in a Si-rich hypoeutectic Al–Si alloy

The combined and separate effects of microstructural scale and silicon phase morphology on the mechanical properties of Al–Si eutectic alloys are investigated here. The Bridgman-type gradient-zone directional solidification method is employed to produce as-cast structures characteristic of the full range of practical (i.e. casting) growth velocities, and the corresponding mechanical properties are characterized by uniaxial tension testing. The results are analyzed in light of previously reported microstructural changes associated with the flake to fiber or “quench modification” transition [1] . Both tensile strength and elongation were found to increase with solidification rate. Application of the Nan–Clarke [2] micromechanical analysis to the Al–Si composite structure, incorporating the strengthening effects of reinforcement-induced dislocations, suggests that the decreasing microstructural scale alone is sufficient to account for the increase in tensile strength with solidification rate. However, the flake to fiber transition was found to have a particular relevance with regard to the fracture behavior of the alloy, increasing tensile elongation and decreasing the overall variability of tensile properties. A maximum in elongation was observed at approximately 600 μm/s, corresponding to the upper threshold of the flake to fiber transition associated with complete disappearance of the flake morphology and dominance of the fibrous structure. These results emphasize the importance of understanding and controlling the flake to fiber transition that occurs with increasing solidification rate in Al–Si eutectic alloys.

The effect of the flake to fiber transition in silicon morphology on the tensile properties of Al–Si eutectic alloys

Heat treating the ductile cast iron produced austempered ductile iron (ADI), which has outstanding mechanical properties that can be varied over a wide range by varying the heat treatment parameters. In the present work a series of test were conducted and the effects of austempering temperature and times onto the material properties was investigated. The machinability of ADI was evaluated by comparing tool life, tool wear rate, cutting forces, and surface finish produced on a job as general criteria. Machinability tests were carried out following ISO 3685: 1993 (E) standard “Tool Life Testing with Single Point Turning Tools”. The cutting force data used in the analyses were gathered by a tool breakage detection system that detects the variations of the cutting forces measured by a three-dimensional force dynamometer. Six pairs of ductile iron specimens, austempered at 300, 350 and 400 °C for 1 and 2 h were tested. The cutting tools used in the tests were coated carbide inserts, ISO SNMG 120408 (K10), clamped on tool holders CSBNR 2525 M12. No cutting fluid was used during the turning operations. During the experiments cutting forces, flank wear and surface roughness values were measured throughout the tool life and the machining performance of ADI having different structures were compared.

The effects of austempering temperature and time onto the machinability of austempered ductile iron

Variation of microindentation hardness with solidification and microstructure parameters in the Al based alloys

The microstructure, hardness, tensile properties and fracture have been studied for the non-modified and modified aluminium (Al) silicon (Si) commercial hypoeutectic alloy. Three modifiers were used being sodium (Na), antimony (Sb) and strontium (Sr). The Sb-modified structure revealed small plate-like Si morphology. The Na and Sr-modified structures exhibited fibrous Si. A slight increase in the hardness values (HV) due to modification was observed. A general increase in the tensile properties was observed due to modification. The tensile properties of the sand mould Sr-modified alloy were significantly higher than those of the Na-modified alloy by 12.7% in proof stress, 16.3% in ductility and 33.3% in toughness. For the metal mould ingots the increase in tensile properties of Sr-modified alloy were respectively: 16.7%, 32.5% and 41.7% compared to a Na-modified alloy. Optical fractography on longitudinal sections near the fracture surfaces of the modified alloys revealed that the crack propagates in the eutectic thus, circumventing the Al-dendrites. The dimple and smooth ripple patterns observed by scanning electron microscope (SEM) on the fracture surface of the Na and Sr-modified alloys suggest a transgranular type of fracture across the grains of the eutectic matrix.

Effect of microstructure on the mechanical properties and fracture of commercial hypoeutectic Al-Si alloy modified with Na, Sb and Sr

Successful casting of three groups of austenitic ductile irons was achieved covering a carbon equivalent (CE) range from 3.51% to 5.04%. The three groups implied the change of C, Si or Ni contents to control the CE%. In case of using Ni element to vary CE%, austenitic ductile iron could be obtained starting from 13.5% up to 34.7% Ni. Generally, the microstructure consisted of graphite nodules embedded in austenitic matrix. Nodule characteristics were affected by the variation of CE%. Nodularity was almost 100% for all tested specimens. Slight decrease in hardness and tensile strength (σu) was observed with increasing the CE%. 0.2% proof stress (σ0.2) showed almost a constant value with increasing CE%. Tensile elongation was mainly increased with increasing CE% with different degrees owing to the alloying element (C, Si or Ni).

C, Si and Ni as alloying elements to vary carbon equivalent of austenitic ductile cast iron: Microstructure and mechanical properties

Microstructure, tensile, impact, hardness, fractography and wear characteristics were investigated for: (1) Austempered ductile iron (ADI); and (2) low alloyed ductile iron. Comparison has been made between the properties of these two types and that of conventional ductile iron. Detailed analysis, of the fracture mode for the 3 types of ductile iron, which failed under tensile and impact testing, were presented using the SEM. The wear properties were determined using pin-on-ring machine, under dry sliding conditions. The variation of mass loss and coefficient of friction with sliding distance, at different loads and speeds were presented and discussed. The wear mechanisms were investigated by means of subsurface observations. Microhardness test was used to study the change in the matrix strength with distance from the worn surface due to plastic deformation.

Effect of microstructure on properties of ADI and low alloyed ductile iron

Results on the effect of solidification cooling rate on the microstructure, mechanical properties and machinability of spheroidal graphite (SG) iron have been presented. The effect of ferritic heat treatment on the same properties has been also investigated. The microstructural observation, tensile properties and hardness values of the present SG iron has been developed. The tool life criterion was used as a measure of machinability. It was found that during turning of SG iron by using a single point cutting tool, its life increased with decreasing the solidification cooling rate for both sand and metal moulds. The tool life was found to be significantly affected by the variation of nodule characteristics. A decrease in tool life due to an increase of nodule count was observed. The tool life was found to be directly proportional to the ductility of SG iron whether for the as cast or ferritic heat-treated ingots.

Metallurgical parameters, mechanical properties and machinability of ductile cast iron

Successful melting and Mg treatment were conducted using a vortex unit which produced spheroidal graphite (SG) Fe ingots having a percentage carbon equivalent (%CE) ranging from 3.782 to 5.240. Microstructure examination revealed graphite nodules embedded in a white matrix (unetched condition). The variation of %CE proved to have a pronounced effect on the nodule characteristics. The nodule count showed a maximum value at %CE of 4.613. For metal-mould ingots it reached a value of 1584 nodules mm−2, while for sand-mould ingots it reached a value of 970 nodules mm−2. Nodule size was found to be inversely proportional to the nodule count for both sand- and metal-mould ingots. The nodularity of all ingots was, in general, higher than 95%. The density of SG Fe was found to decrease gradually (at %CE=3.782) from 7242 to 6969 kg m−3. The modulus of elasticity (E) showed a boat-like curve having minimum values of 189 and 192 GPa for the sand and metal moulds, respectively.

N. Fatahalla

Papers

Effect of microstructure on the mechanical properties and fracture of commercial hypoeutectic Al-Si alloy modified with Na, Sb and Sr

C, Si and Ni as alloying elements to vary carbon equivalent of austenitic ductile cast iron: Microstructure and mechanical properties

Effect of microstructure on properties of ADI and low alloyed ductile iron

Metallurgical parameters, mechanical properties and machinability of ductile cast iron

Effect of the percentage carbon equivalent on the nodule characteristics, density and modulus of elasticity of ductile cast iron