Thermal-rate Treatment Research Articles

The effect of melt thermal-rate treatment on precipitation hardening and mechanical properties of Al–Si–Mg alloys

In this study, we investigate the age-hardening behavior and mechanical properties of direct chill (DC)-cast Al–10Si-0.35 Mg alloys subjected to melt thermal rate treatment (TRT). Our findings reveal that TRT refines the microstructure and precipitation morphology. Grain analysis indicates the prevalence of twin dendritic grains in both TRT and non-TRT (NTRT) alloys during casting, with the TRT billet exhibiting smaller grains. The microstructural analysis demonstrates that TRT reduces the size of secondary dendrite arm spacing and eutectic phases while ensuring a uniform distribution of intermetallic particles. The precipitation mechanism in both alloys remains consistent, with the TRT alloy exhibiting a higher density of fine precipitates. Additionally, we observe a novel coprecipitation mechanism of Si and β″ phase, attributed to a lower misfit between (003)β″ and (011)Si compared to that between (003)β″ and (0 2‾ 0)Al. Furthermore, the TRT alloy displays slower precipitation kinetics due to homogeneous solute distribution, resulting in higher activation energy for precipitation nucleation. Consequently, a single age-hardening peak is observed in TRT alloys during aging. TRT alloys exhibit higher hardness and tensile strength after artificial aging at 190 and 210 °C, while maintaining comparable elongation to NTRT alloys. Theoretical calculations of precipitation strengthening also show higher values for TRT alloys, consistent with experimental results. Thus, our findings comprehend the underlying mechanisms of melt treatments crucial for improving precipitation hardening behavior and mechanical properties of Al–Si–Mg alloys.

Melt thermal-rate treatment for uniform solute distribution and improved mechanical properties of an Al-Zn-Mg-Cu alloy prepared by direct-chill casting

Melt thermal-rate treatment (MTRT), a promising technique for improving microstructure uniformity, has been rarely applied in direct-chill (DC) casting. In this study, we investigated the effects of MTRT on the microstructure and mechanical properties of an Al-Zn-Mg-Cu alloy billet prepared using DC casting. Results indicate that MTRT improved the uniformity of solute distribution in the Al matrix, thereby enhancing mechanical properties such as hardness, tensile strength, and ductility. In particular, yield strength, ultimate tensile strength, and elongation of the near-surface region of the billet increased from 250 to 274 MPa, from 319 to 393 MPa, and from 2% to 8%, respectively. It has been reported that twinned dendrite grains (TDGs) form on the surface of billets because of directional solidification or DC casting at high cooling rates. However, this study reveals that the formation of TDGs was induced in the central region of the billet by MTRT. Furthermore, the effects of TDGs on the mechanical properties are evaluated and compared with those of regular grains of MTRT billets. Overall, these findings suggest that MTRT is an efficient technique used to improve the mechanical properties of Al alloys fabricated using DC casting.

X-ray computed tomography of cast metal matrix composites

The development of new cast metal matrix composites and technological processes for their production are inextricably linked with the need to improve the methods of quantitative non-destructive testing. In this work, the features of the spatial structure of cast in-situ metal matrix composites (on example of the Al – Mg2Si system) were studied using X-ray computed microtomography. The parameters of tomographic scanning were optimized to identify structural components with close ranges of radioparency. The rational selection of the scanning parameters of the samples made it possible, during the subsequent computer processing of the slice sets, to clearly identify the structural constituents of the metal matrix composites depending on the gray levels in their comparison with the characteristic morphology of the observed constituents (primary Mg2Si crystals, pseudobinary eutectic, compounds of impurity elements). The total volume of porosity in the studied samples of Al + 15 wt.% Mg2Si composites after melt thermal-rate treatment at 900 °C did not exceed 0.05 mm3, which corresponds to a porosity content in the sample of 0.13 vol.%. The presented results show the significant potential of tomography in the study of the structural and morphological characteristics of composite materials and internal defects in cast products made from them. This research was funded by the Russian Science Foundation (Project № 20-19-00687).

Influence of parameters used for melt processing by nanosecond electromagnetic pulses on the structure formation of cast aluminum matrix composites

The paper focuses on establishing the effect of nanosecond electromagnetic pulses (NEPs) with different amplitudes on the formation of the structure of cast aluminum matrix composites of the Al–Mg2Si pseudobinary system with hypoeutectic (5 wt. % Mg2Si) and hypereutectic (15 wt. % Mg2Si) compositions. As the NEP generator amplitude in composites containing 5 and 15 wt. % Mg2Si increases, the matrix alloy structural components (α-solid solution and eutectic) are refined, while no significant differences in the sizes and morphology of Mg2Si primary crystals were observed in the hypereutectic range of compositions. Presumably, the observed nature of the NEP effect on the structure of composites in the hypereutectic region of compositions is associated with the features of their crystallization behavior. The temperature range of the L + Mg2Si two-phase region presence is much lower than NEP irradiation temperatures. Apparently, this is the reason why NEPs have no effect on the thermodynamic state of Mg2Si primary crystal/melt interfaces. It was shown that a promising option for the simultaneous modifying effect on all structural components of Al–Mg2Si aluminum matrix composites (solid solution, eutectic, Mg2Si primary particles) is a combination of thermal-rate treatment and irradiation of melts by NEPs, as well as additional melt processing by NEPs during crystallization.

Effects of thermal-rate treatment and modification of Ce on the microstructure and properties of A356 alloys

In this study, the effects of thermal-rate treatment (TRT) and modification of Ce on the microstructure and mechanical properties of A356 alloy were investigated. The results showed that the microstructure of A356 alloy was improved after TRT and modification of Ce. The α-Al was refined significantly and the eutectic Si transformed from needle-like shape to granular-like shape. When the content of Ce increased to 0.5%, the grain size of α-Al of A356 alloy began to increase and the dendrites became coarse. When the Ce content was 0.4%, the tensile strength and yield strength of A356 alloy were 183MPa and 124 MPa, respectively. The mechanism of (TRT+Ce) on the grain refinement of α-Al and modification of eutectic Si was discussed.

Improving the wear resistance of cast aluminum alloys by the melt thermal-rate treatment

The method of the melt thermal-rate treatment has been successfully tested to increase the macrohardness and abrasive wear resistance of a low-alloy cast aluminum alloy of the Al-Mg-Si system. It was found that an increase in the melt superheating temperature to 900 °C with subsequent isothermal holding and fast cooling to the pouring temperature leads to a decrease in weight loss from 0.359 to 0.324 in comparison with the initial state, which corresponds to an increase in the coefficient of relative wear resistance to 1.11. A good correlation has been found between wear resistance and macrohardness of treated alloys. Application of the proposed approach will increase the service life of aluminum parts exposed to various abrasive effects, however, to further increase the wear resistance, it is recommended to obtain a reinforced composite structure in the Al-Mg-Si system using the melt thermal-rate treatment.

Grain refining effects of the melt thermal-rate treatment and Al-Ti-B-Y refiner in as-cast Al-9Si-0.5Mg alloy

This paper investigated the effects of melt thermal-rate treatment and Al-3Ti-3B-1Y grain refiner on the microstructure and mechanical properties of hypoeutectic Al-9Si-0.5Mg alloy. The results showed that the grain refining effect of the melt thermal-rate treatment was more remarkable than that of Al-3Ti-3B-1Y grain refiner. After the appropriate melt thermal-rate treatment (MTRT), the microstructure and mechanical properties of alloy were significantly optimized and the α-Al phase changed from dendritic grains to columnar grain. The MTRT technique compound with Al-3Ti-3B-1Y grain refiner could further refine the microstructure. In addition, the change of vacancy concentration induced the morphology change of α-Al phase. The mechanism of the refinement and the toxic effect of Y element were clarified, which provide a reference for developing a new type of Al-Ti-B-RE grain refiner and the melt treatment method.

Effect of Parameters of Thermal-Rate Treatment of Melt on Iron-Containing Phases in Alloy Al – 15% Si – 2.7% Fe

The effect of the parameters of thermal-rate treatment of melt on the iron-containing phases in alloy Al – 15% Si – 2.7% Fe is considered. The structure and mechanical properties of the alloy are determined after a thermal-rate treatment conducted at different temperatures of the melt, different pouring temperatures, and different holds at the pouring temperature. The optimum variants of thermal-rate treatment of melt for alloy Al – 15% Si – 2.7% Fe are chosen.

Effects of Melt Thermal-Rate Treatment and Modification of Y on Zn-27Al Alloy

In this paper, the effects of melt thermal-rate treatment (MTRT) and modification of Y on the microstructure and mechanical properties of Zn-27Al alloy are discussed. The experimental results suggest that the microstructure can be refined and the mechanical properties can be improved with the MTRT technique. The effect of grain refinement achieves the best when the melt temperature is up to 830°C, the tensile strength of alloy is 452 MPa and the hardness is 123 HB, each measure increasing by 13.6% and 7.1% compared with the untreated alloy, respectively. When the alloy is treated with the MTRT + Y technique, the mechanical properties of the alloys cannot improve compared with that of the alloy treated with MTRT. The mechanism of the effects of MTRT and Y are discussed.

Effects of Melt Thermal-Rate Treatment on Fe-Containing Phases in Hypereutectic Al-Si Alloy

In this paper, effects of melt thermal-rate treatment (MTRT) on Fe-containing phases in hypereutectic Al-Si alloy were investigated. Results show that MTRT can refine microstructures and improve castability, mechanical properties, wear characteristics, and corrosion resistance of Fe-containing Al-Si alloy. When Al-15Si-2.7Fe alloy is treated with MTRT by 1203 K (930 °C) melt: coarse primary Si and plate-like Fe-containing phase both can be refined to small blocky morphology, and the long needle-like Fe-containing phase disappears almost entirely; ultimate tensile strength and elongation are 195 MPa and 1.8 pct, and increase by 12.7 and 50 pct, respectively; and the wear loss and coefficient of friction decrease 7 to 17 and 24 to 30 pct, respectively, compared with that obtained with conventional casting technique. Corrosion resistance of the alloy treated with MTRT by 1203 K (930 °C) melt is the best, that is it has the lowest i corr value and the highest E corr value. Besides, effects of MTRT on Al-15Si-xFe (x = 0.2, 0.7, 1.7, 3.7, 4.7) alloys were also studied, MTRT can only refine microstructure and improve mechanical properties of Al-15Si alloy with 0.7 to 3.7 pct Fe content greatly in the present work.

Effects of melt thermal rate treatment and modification of P and RE on hypereutectic Al–Si–Cu–Mg alloy

In the present paper, a new melt treatment technique is proposed, and its effects on hypereutectic Al–18Si–1·5Cu–0·6Mg alloy are investigated. Results show that the mechanical properties of Al–18Si–1·5Cu–0·6Mg alloy are improved remarkably, and primary Si and eutectic silicon can be well refined. The average size of primary Si decreases from ∼100 to <10 μm, and eutectic silicon turns into granular shape from coarse long acicular morphology. The tensile strength and hardness of the alloy increase by 55·14 and 70% respectively, compared with that obtained by the conventional casting technique. In addition, the resistivity–temperature characteristic of the Al–18Si alloy melt was investigated through the resistivity–temperature test, and the melt structure state information was the basis of the melt thermal rate treatment.

Study of Melt Thermal-Rate Treatment and Low-Temperature Pouring on Al-15%Si Alloy

Under the condition of melt thermal-rate treatment (MTRT) and low-temperature pouring (LTP), the tensile properties of Al-15%Si alloy are improved, the average size of primary Si is refined to about 20 μm from about 50 μm, and eutectic silicon can be well modified. The ultimate tensile strength and elongation are 201 MPa and 3.5%, and these values increase by 12% and 25%, respectively, compared with that obtained by conventional casting technique. The Al-15%Si alloy modified with Sr and RE additions was also studied for comparison purposes. The tensile properties of the Al-15%Si alloy treated with MTRT + LTP are superior to those modified with Sr or RE addition individually. The eutectic growth temperature difference between modified and unmodified melts was used to indicate the modification level. The modification effect of MTRT + LTP on Al-15%Si alloy is better than that modified with Sr or RE addition.

Effects of Thermalrate Treatment Technique on Microstructure and Mechanical Properties of Hypoeutectic Al–Si Alloys

In this study, effects of thermalrate treatment (TRT) technique on microstructure and mechanical properties of hypoeutectic Al–Si alloys with addition of Ti were studied. The superheating temperatures of the melt were ascertained based on the DSC result. The results show that when the alloy castings in sand mold were treated with TRT technique at the superheating temperature of 930 °C, α-Al changes into smaller equiaxial crystals from coarse dendrites, and hardness of the alloy increases by 12.7 %, compared to that of the alloy treated with conventional casting technique. In addition, the supercooling increases to 8.5 °C and the characteristic temperatures of eutectic solidification are all the lowest with TRT technique at the superheating temperature of 930 °C. As holding time increases at the pouring temperature of 730 °C in TRT at the superheating temperature of 930 °C, the effects on microstructure and mechanical properties of the alloy casting in sand mold decrease. TRT technique plays a limited role in the alloy casting in permanent mold.

Grain Refinement of Zn-50Al Alloy through the Addition of Zn–Al-Ti-B-C Master Alloy and Melt Thermal-Rate Treatment

In this paper, two types of Zn-Al-Ti-B-C master alloys were produced by a two-step method and were found to have good refinement effect for Zn-50Al alloy. SEM results show that TiC and TiB2 particles act as the nucleating center of α-Al grains in Zn-50Al alloy. The presence of TiAl3-xZnx phase in the matrix of Zn-Al-Ti-B-C master alloy was found to further enhance the refinement effect. The melt thermal-rate treatment process present good grain refinement effect for Zn-50Al alloy and it was further promoted by the addition of Zn-Al-Ti-B-C master alloy into Zn-Al matrix.

Effects of complex modificating technique on microstructure and mechanical properties of hypereutectic Al–Si alloys

In this article, the structure of Al-18Si alloy was modified by thermal-rate treatment technique at 930 °C based on the DSC result. The mechanical properties of Al–18Si alloy were improved remarkable by a complex technique with alloying and thermal-rate treatment. A new treating technique named as complex modificating technique was proposed, and the performance of this technique on Al–18Si–1.5Cu–0.6Mg alloy was investigated. The results show that primary Si can be refined when Al–P master alloy was added into the melt at 770 °C after thermal-rate treatment. Compared with the conventional casting technique by which the melt of alloy was unmodified, better refinement effect can be obtained with the combination of alloying and complex modificating technique: the size of primary Si is decreased from 66 to 16 μm, the tensile strength increased by 75.94% and the brinell hardness by 66.59%. Moreover, the mechanism of the complex modificating technique was also discussed.

Microstructure and Mechanical Behaviors of AZ91 Magnesium Alloy with Thermal Rate Treatment Technique

Microstructure and mechanical behaviors of AZ91 cast magnesium alloys with melt superheating and thermal rate treatment technique were studied. Alloy grains thicken at 820°C and refine at 870°C when they contains Mn element and the crucible had no coating on the internal surface. Moreover, the strengthening γ phase is more dispersive and uniform at 870°C. Thermal rate treatment significantly improved the microstructure, mechanical behaviors and casting quality of AZ91 alloy as microstructure of AZ91 alloy reserves some characteristics of the high temperature melt.

Effect of TRT process on GFA, mechanical properties and microstructure of Zr-based bulk metallic glass

AbstractSeries of rod samples of Zr55Al10Ni5Cu30 alloy were prepared by magnetic suspend melting and copper mold suction casting method. The effect of thermal rate treatment (TRT) process on glass forming ability (GFA), mechanical properties and microstructure of Zr-based bulk metallic glass were investigated. It shows that GAF, mechanical properties and microstructure of as-cast Zr55Al10Ni5Cu30 BMGs alloy to a large extent is related to TRT process. GFA and thermal stability of as-cast Zr55Al10Ni5Cu30 alloy increase when overheating temperature increases. Supercooled liquid region ΔTx and parameter γ increase from 73 K to 89 K, from 0.413 to 0.417, respectively, when casting voltage increases from 7 kV to 10 kV. And a threshold overheating temperature is found for the fully amorphous structure, below which it may have an intersection with the crystallization position. It is found that the compressive strength increases and the compressive plasticity slightly decreases when overheating temperature increases. However, the compressive strength and the compressive plasticity simultaneously increase to 1.91 MPa and 2% when casting voltage increases to10 kV.

Influence of thermal rate treatment and low temperature pouring on microstructure and tensile properties of AlSi7Mg alloy

The combination of thermal rate treatment and low temperature pouring was proposed in the present work, and the effects of the novel melt thermal treatment on microstructure and tensile properties of AlSi7Mg alloy have been investigated. The grain size and microstructure of AlSi7Mg alloy were examined by optical microscopy (OM) and scanning electron microscopy (SEM). It was found that the grain size obviously reduced and the growth of the columnar dendrites changed into equiaxed ones by low temperature pouring, especially the novel melt thermal treatment, by which a maximum microstructure refining effect could be obtained. The refinement can be attributed to the multiplication of the nuclei in the melt. Furthermore, the morphology of eutectic silicon changed little, but the size of silicon phase was finer due to the refinement of the grain size and higher cooling rate. Because of the refinement of the grain size and eutectic silicon, the tensile properties were improved, and the ultimate tensile strength and elongation increased by 11.7% and 35.3%, respectively.

Effect of melting technique on the microstructure and mechanical properties of AZ91 commercial magnesium alloys

The microstructure of AZ91 magnesium alloy refined by thermal rate treatment technique (TRT), and the β-phase is more dispersive and uniform. Though the superheating microstructure is finer than microstructure with TRT technique, TRT technique can reduce the casting defects such as hot tears and shot run, more suits the practical requirement. The microstructure of AZ91 alloy keeps some characteristics of the high temperature melt after TRT. On the other hand, the microstructure of AZ91 magnesium alloy containing excess element Fe could not be refined and even be coarsened after thermal rate treatment, which brings on the decrease of mechanical properties as the results of interdendritic shrinkage microporosity and coarse β-phases. These different effects of TRT on AZ91 magnesium alloys can be related to the presence of non-equilibrium condition in the mixed melt structure through mixing the high superheating temperature and low temperature melts in TRT technique.

Thermal-rate treatment and critical thickness for formation of amorphous Al 85Ni 10Ce 5 alloy

The effects of a thermal-rate treatment technique on the critical thickness of glass formation for an Al 85Ni 10Ce 5 alloy melt have been investigated. The amorphous ribbon of the alloy with a thickness of 300 μm is obtained using a single-roller melt-spinning technique by the thermal-rate treatment, while that of 50 μm is obtained at conventional melt superheating condition. The experiment shows that the coordination numbers of the Al 85Ni 10Ce 5 alloy melt decreases from 12 to 9 with increasing melt temperature from 900 to 1200 °C. The relationship between the coordination numbers, the first position of the main peak of the alloy melt and the critical cooling rate for getting amorphous alloys has been discussed.