Cooling Slope Research Articles

Microstructure Evolution of A356 Aluminum Alloy Produced by Cooling Slope Method

In this work the cooling slope (CS) method was employed to produce the A356 feedstock in semisolid processing. The dendritic primary phase in the conventionally cast A356 alloy has transformed into a non-dendritic one in ingots cast over a cooling plate with (625°C, 650°C and 680°C) superheat. After pouring, the melt which became semisolid at the end of the plate was consequently poured into cylindrical steel mold with the various mold temperatures of (25°C, 200°C, 400°C). In this study, the cooling slope was adjusted at 50o with respect to the horizontal plane and 500mm length. It was found that the pouring and mold temperature affect the size and morphology of α-Al phase.

Formation of Globular Microstructure in A380 Aluminum Alloy by Cooling Slope Casting

Thixoforming and related semi-solid processing (SSP) methods require thixotropic materials. One of the many SSP techniques is the cooling slope (CS) casting process, which is simple and has minimal equipment requirements, and which is able to produce feedstock materials for semisolid processing. When the feedstock is reheated to the semisolid temperature range, non-dendritic, spheroidal solid particles in a liquid matrix suitable for thixoforming are obtained. In this study, equipment for the CS technique was first established, and then the effects of the pouring temperature and inclined slope angle on the microstructures of A380 aluminum alloy (ISOAlSi8Cu3Fe) were studied. Optimum parameters for thixoforming experiments were selected, and it was found that the microstructure produced by the inclined plate depended on its angle and the pouring temperature.

The Effects of Cooling Slope Casting and Isothermal Treatment on Wear Behavior of A380 Alloy

In this study, A380 aluminum alloy feedstock produced with cooling slope casting was exposed to isothermal treatment to obtain a globular microstructure which is a key feature for semisolid forming. The dendritic primary phase in the conventionally cast A380 alloy has readily transformed into a non-dendritic one in ingots cast over a cooling plate from pouring temperatures between 615, 630 and 650 °C. After the casting process, isothermal treatment was carried out at 565 °C in induction unit. Isothermal treatment yields a globular microstructure. To determine the tribological properties of this alloy, a pin-on-disc tribometer was used to carry out tribological tests under dry sliding conditions. The results showed that both cooling slope casting and isothermal treatment has an effect on tribological properties.

Preparation of Semisolid A356 Alloy by a Cooling Slope Processing

In order to obtain the non-dendritic feedstock for the semisolid forming process, a cooling slope processing was used. In this work, the effects of the angle, length of cooling slope and pouring temperature on the microstructure of A356 aluminum alloy were investigated. It showed that these parameters affect the size and morphology of α-Al phase to some extent. The results indicate that a pouring temperature of 650°C and a cooling slope with 45° in angle and 50 cm in length are the optimum parameters for preparing fine and globular grain structures. To eliminate the solidification shell formed in the surface of cooling slope, a nitride dope was coated on the surface of the cooling slope.

Coarsening rate of microstructure in semi-solid aluminium alloys

The rate of microstructural coarsening of recrystallisation and partial melting (RAP) and cooling slope (CS) processed materials in the semi-solid state is compared with rates found in the literature. The rate of coarsening depended on the liquid fraction but RAP route 2014 alloy with 37% liquid coarsened slightly more slowly than the CS route 2014 alloy with a lower liquid fraction of 17%, contrary to expectations. For the CS route, an increase in liquid fraction resulted in faster coarsening. A modified 2014 alloy with Fe, Mn and Zn stripped out of the composition gave a relatively high coarsening rate. The coarsening rate was also relatively high for CS 201 alloy in comparison with either RAP 2014 or CS 2014. Low coarsening rates are thought to be associated with the presence of particles which inhibit the migration of liquid film grain boundaries. This could be the result of pinning or of the liquid film impeding diffusion at the boundary.

Semisolid Microstructure Evolution during Cooling Slope Casting under Vibration of A380 Aluminum Alloy

This study is concerned with the influence of the vibration at a specific frequency to the inclined plate during cooling slope casting. A380 aluminum alloy was employed in the present work. The alloy was poured from the inclined plate with an angle of 60°and a length of 500 mm at a pouring temperature of 630°C. The pouring was carried out on an inclined plate with and without vibration. Microstructures of specimens obtained from both conditions were examined. Grain size analysis of specimens was carried out. Experimental results showed that the application of vibration affected the microstructure. Hence, it was determined that the application of vibration increased the nucleation and led to more breaking of dendrite arms. In this study, the convection of melt by vibration played an important role on formation of non-dendritic primary Al-particles.

Microstructural coarsening of semi-solid aluminium alloys

Semi-solid metal processing involves processing metallic alloys between the solidus and the liquidus. The microstructure must be non-dendritic and consist of spheroids of solid in a liquid matrix. Two potential routes to suitable starting material are recrystallisation and partial melting (RAP) and cooling slope (CS). Here the microstructural coarsening of such materials in the semi-solid state is compared with rates in the literature. A slightly lower coarsening rate was observed for RAP route 2014 alloy with 37% fraction liquid than for CS route 2014 alloy with 17% fraction liquid despite the higher fraction liquid for the former. For the CS route, an increase in fraction liquid gave a higher coarsening rate. A relatively high coarsening rate was observed in a modified 2014 alloy with the Fe, Mn and Zn stripped out of the composition and a relatively low Si content. The coarsening rate was also relatively high for alloy 201 prepared by the CS route compared with alloy 2014 either by RAP or CS. It is likely that relatively low coarsening rates are associated with the presence of particles which are inhibiting the migration of liquid film grain boundaries, either through a pinning mechanism or through impeding diffusion through the liquid film at the boundary.

A357 thixoforming feedstock produced by cooling slope casting

Cooling slope (CS) casting process was employed in the present work to produce A357 thixoforming feedstock. The dendritic primary phase in the conventionally cast A357 alloy has readily transformed into a non-dendritic one in ingots cast over a cooling plate from pouring temperatures between 620 and 640 °C and with cooling lengths between 200 and 400 mm. Dissipation of the melt superheat required longer cooling lengths for higher pouring temperatures. Primary phase in the ingots thus produced has attained a globular morphology in only as much as 5 min during isothermal holding at 580 °C. The minor effect the pouring temperature and the cooling length had on the CS-cast morphologies was not evident after reheating, implying that a wide range of CS casting parameters are capable of providing the required microstructural features for thixoforming.

In Situ Observation of SSM Microstructure Formation during Cooling Slope Casting of an NH<sub>4</sub>Cl-H<sub>2</sub>O Alloy with Vibrating the Slope

Vibrating the slope during cooling slope casting of a metallic alloy has shown helpful for causing the microstructure more spherical and thinner in a previous research by the present authors. This paper gives results from a direct observation of the SSM microstructure formation during cooling slope casting of an NH4Cl-H2O alloy with vibrating the slope. It is found that the vibration exerted to the slope can break down the solidification shell formed at the surface of the slope through rapid chilling and produce effectively fine globular grains in the microstructures. The main factors affecting the fine grain formation include the chilling extent, frequency and amplitude of the vibration of the slope, and the superheat of the alloy melt, respectively. The higher vibration frequency and amplitude, the lower superheat of the alloy melt, and the lower chilling temperature will help the formation of finer globular grains.

Production of AA6082 Feedstock for Forming in the Semi-Solid State

Thixoforming offers the possibility of forming complex aluminum parts with a superior quality and a reduction of processing steps. The production of a fine, equiaxed, globular microstructure is essential for thixoforming. Strain Induced Melt Activation (SIMA) and the Cooling Slope (CS) casting processes were employed to produce AA6082 thixotropic feedstock in the present work.. SIMA process produces such a microstructure through recrystallization of heavily deformed billets and a subsequent heat treatment in the mushy zone. Molten metal with a suitable superheat is cast over a water-cooled, inclined metal plate into a permanent mould to produce the thixotropic billet in the CS casting route. The effect of cold work and heating temperature and time were investigated for the SIMA process where as the effect of CS length, casting temperature on the final microstructures were investigated for a fixed set of heating conditions in the CS casting route.

Semi-Solid Process of Cast Iron with Combination of Cooling Slope and Pressurization

Semi-Solid Process of Cast Iron with Combination of Cooling Slope and Pressurization

Microstructural evolution and tensile mechanical properties of thixoformed high performance aluminium alloys

Commercial thixoforming is generally based on conventional aluminum-based casting alloys such as A356 and A357. However, these alloys do not give such high mechanical properties as the alloys that are conventionally wrought such as 2000, 6000 and 7000 series or the high-strength aluminium casting alloys such as 201. In this paper, 201, 2014, 6082, 7075, 7010 and ‘modified’ versions of 2014 (3.87 wt.% Cu, 0.6 wt.% Mg, 0.14 wt.% Si), 6082 (1.29 wt.% Si, 1.21 wt.% Mg) and 7075 (6.01 wt.% Zn, 3.99 wt.% Mg, 2.06 wt.% Cu, 0.12 wt.% Si) were thixoformed. The recrystallisation and partial (RAP) melting route and the cooling slope (CS) casting route were used to obtain the semi-solid feedstock for thixoforming. Microstructural evolution during partial melting was studied at temperatures where the amounts of liquid were comparable for the various alloys. Tensile mechanical properties of thixoformed parts in the T6 condition were determined and compared with those of conventionally wrought alloys and thixoformed high performance aluminium alloys from the literature. The tensile properties of the thixoformed alloy 201 show a significant improvement over permanent mould casting and the tensile properties of the thixoformed 2014, with an optimised heat treatment schedule, were close to those of forged 2014 but with lower elongation to fracture. Good elongation to fracture (19.6%) was obtained for thixoformed ‘modified’ 2014 in the T6 condition, with a yield strength of 270 MPa and a tensile strength of 408 MPa. This yield strength is significantly short of the target wrought 2014 value and the tensile strength is a little short. The elongations to fracture (24.4 and 12.3%) are satisfactory for alloy 6082 and ‘modified’ 6082 but yield strength and tensile strength need to be increased to achieve the wrought 6082 target. The tensile properties for 7075 thixoformed from starting material produced by the recrystallisation and partial melting route are a little better than those of 7075 thixoformed from starting material produced on the cooling slope. Both routes give values close to the wrought target 7075. The yield strength and tensile strength for ‘modified’ 7075 and 7010 are quite close to the wrought target.