Constrained Rod Research Articles

Influence of zinc and silver additions on hot tearing susceptibility of Mg-14Gd-0.4Zr alloy

The effects of 1Zn and/or 2Ag additions on the hot tearing susceptibility (HTS) of Mg-14Gd-0.4Zr (wt%) alloy were studied. The HTS was evaluated by both theoretical predictions using Kou's criterion and experimental observations based on the in situ force-temperature recorded constrained rod casting (ISFTCRC) method. The results show that the order of HTS from high to low is Mg-14Gd-2Ag–1Zn-0.4Zr, Mg-14Gd-2Ag-0.4Zr, Mg-14Gd-1Zn-0.4Zr and Mg-14Gd-0.4Zr. Adding 1Zn and/or 2Ag changes the solidification path and the solidification interval, which affects the hot tearing susceptibility. Alloying elemental 1Zn slightly increases the solidification interval and the temperature range in the square root of the solid phase fraction (ƒs1/2) range of 0.949–0.995, resulting in a slight increase in the hot tearing susceptibility. The addition of 2Ag drastically widens both the solidification interval and the temperature range in the ƒs1/2 range of 0.949–0.995, thus significantly increasing the hot tearing susceptibility. Compared to the addition of 2Ag alone, the broadening degree of both the solidification interval and the temperature range in the ƒs1/2 range of 0.949–0.995 is greater by adding the composite 2Ag/1Zn, which further promotes the occurrence of hot tearing. A narrower solidification interval and a temperature range in the ƒs1/2 range of 0.949–0.995 result in a lower hot tearing susceptibility.

Evaluation of Horizontal and Vertical Constrained Rod Casting Mold on Hot Tearing Susceptibility of Al-Cu Alloys

Evaluation of Horizontal and Vertical Constrained Rod Casting Mold on Hot Tearing Susceptibility of Al-Cu Alloys

A И-Shaped Curve of Hot Tearing Susceptibility in Magsimal®-59-Based Alloys

The hot tearing susceptibility of Al-6Mg-xSi (x = 0-6.0 wt.%) alloys was studied using constrained rod casting. Addition of Si content resulted in double ternary eutectic reactions and then changed the freezing range and eutectic liquid fraction greatly, which made the hot tearing susceptibility show a И-curve with the increasing of Si content. The И-curve was obviously different from the λ-curve that supported by most researchers.

Characterization Analysis of A304 and A380 Aluminum Alloys

The hot tearing susceptibilities of an Al–Si based alloy were investigated for hot tearing characteristics. The experimental studies were conducted using a newly developed enhanced constrained rod casting method that enables real-time measurements of the contraction load developed in the casting and the temperature variations during solidification as a function of time. A304 and A380 casting alloys were selected to study hot tearing characteristics at pouring temperatures of 700 °C, 750 °C, and 800 °C. The study showed that hot tearing was not observed in measurement rod of A304 and A380 casting alloys. However, hot tearing was observed in the constrained rods A and B of A380 casting alloy at 750 °C. A304 alloy showed higher resistance to hot tearing at a casting temperature below 750 °C.

A Critical Conception of Hot-Tearing Susceptibility: How Controlled Diffusion Solidification Enables Shape-Casting with Wrought Aluminum Alloys

Instrumented Constrained Rod Casting (CRC) method and the Controlled Diffusion Solidification (CDS) process were used to study the high susceptibility of the aluminum alloy AA 7068 to hot-tearing. A precise analysis of the measured hot-tearing curves is provided considering the casting design and different feeding mechanisms. Scanning Electron Microscopy was used to study the hot-tear surfaces. It was found that the solidification of the eutectic liquid at the film stage and the phenomenon of solid-feeding strongly affects the hot-tear formation. The early formation of an absorbed eutectic layer on the primary phase due to low rate of back-diffusion is proposed to explain the loss of ductility at the film stage. The layer can serve as an efficient substrate for the eutectic nucleation and growth, hence its formation can advance the eutectic solidification. The isolation of liquid eutectic by its partial solidification results in development of solid-feeding stresses breaking the solid eutectic and provide the required tearing initiators. By increasing the back-diffusion rate, the CDS process avoids formation of the adsorbed solid layer which postpones eutectic solidification and thereby mitigating the hot-tearing susceptibility.

Effect of Al Content on Hot-Tearing Susceptibility of Mg-10Zn-xAl Alloys

The hot-tearing susceptibility of Mg-10Zn-xAl (x = 0, 2, 5, and 7) alloys was studied using constrained rod casting installed with a load cell, thermocouple, and data-management system. Addition of Al content reduced the freezing range and increased the liquid fraction at the end of the primary stage of solidification, during the vulnerable period of alloy solidification. Eutectic healing was observed in alloys containing Al cast at a higher initial mold temperature due to near-equilibrium solidification. Grain refining was confirmed at the microstructural level due to addition of Al. The results also suggested that increasing Al content enabled hot-tearing resistance of Mg-10Zn alloy by facilitating liquid feed for the strain developed during the mid-stage of solidification (0.65Fs to 0.74Fs). Experimental results were compared with Pandat’s simulation results to predict the occurrence of hot tearing in Mg-10Zn-xAl alloys. This indicated that Pandat’s solidification curve could be used to determine the hot-tearing nature of Mg-Zn alloys. The recently proposed hot-tearing criteria of Kou and Clyne–Davie roughly agreed with the experimental results, but did not perfectly predict the influence of different casting conditions.

Hot Tearing Susceptibility of AA3000 Aluminum Alloy Containing Cu, Ti, and Zr

Severe hot tearing has been observed during DC casting of modified AA3000 alloys with additions of Cu, Ti, and Zr, although these alloys are regarded as rather easy to cast. Extensive studies have been performed on both synthetic and industrial AA2000, AA6000, and AA7000 alloys, but less data are available for AA3000 alloys. This work was thus initiated to investigate the hot tearing susceptibility of AA3000 alloys with varying alloy element content using constrained rod casting molds. The results showed that the Cu and Fe content have a major impact on hot tearing resistance, while the effects of Zr and Ti are minor. Cu in a range from 0.3 to 1.2 wt pct significantly increased the hot tearing tendency. This is due to the existence of high eutectic fractions at low temperatures, as well as porosity formation associated with bad feeding at the end of solidification. A strong cracking tendency was observed below an Fe content 0.2 wt pct owing to decreased precipitation of the Al6(Mn, Fe) phase. It was found that primary Al6(Mn, Fe) phases lead to early bridging between the grains, which reinforces the alloy during the vulnerable temperature range for hot tearing. Zr and Ti additions weakly enhanced or reduced hot tearing severity, respectively.

Influences of Rod Diameter and Sand-Mould Strength on Hot Tearing in Mg WE43A Constrained Rod Castings

Under conditions of changing sand-mould strength and rod diameter, hot tearing susceptibility of Mg WE43A alloys was studied using constrained rod casting solidified in a sand mould. Variations of temperature and shrinkage force with time during solidification of Mg WE43A alloy were recorded by means of a thermocouple and a force sensor. Susceptibility to hot tearing at hot section was decreased with increasing rod diameter from 10 mm to 20 mm. The rod with 10 mm diameter fractured, and the rod with 15 mm diameter presented hot tearing. No hot tearing was noted for the rod with 20 mm diameter. For the resin content of 1%, 1.5%, 2%, 2.5% and 3%, the tensile strength of sand mould was measured as 0.12, 0.18, 0.28, 0.17 and 0.15 MPa, respectively. The casting fractured at hot spot position for the sand mould with strength of 0.12 MPa. Hot tearing occurred at hot spot for the sand mould with strength of 0.15 MPa. No hot tearing was found at hot spot for the sand mould with strength of 0.28 MPa. The present research confirms that increasing the sand-mould strength and avoiding the entrapment of sand particles and the formation of gas pores during casting increase the resistance to hot tearing.

The effects of degassing, grain refinement & Sr-addition on melt quality-hot tear sensitivity relationships in cast A380 aluminum alloy

Abstract Hot tearing tendency of A380 with various element additions (Sr, Sr+Ti, Ti, B and B+Sr) was investigated. Constrained rod casting (CRC) hot tearing test method was used to characterize the hot tearing sensitivity. Reduced pressure test (RPT) samples were produced from each condition and all trials were repeated three times. Number density of pores on the cross section of RPT samples was calculated via digital image processing and statistical analysis was carried out. Microstructure analysis was carried out to observe the effect of alloying elements. Hot torn cross sections were subjected to SEM analysis. It was found that in aluminum alloys, the most deleterious defects, bifilms that are the cause of many defects, play an important role in initiating the hot tearing during solidification. It is important to note that the shape, size and distribution of bifilms are too complex. They act as heterogeneous nucleation site for liquid to separate and thus increase hot tearing.

Freezing Range, Melt Quality, and Hot Tearing in Al-Si Alloys

In this study, three different aluminum-silicon alloys (A356, A413, and A380) that have different solidification morphology and solidification ranges were examined with an aim to evaluate the hot tearing susceptibility. T-shape mold and Constrained Rod Casting (CRC) mold were used for the characterization. Reduced Pressure Test (RPT) was used to quantify the casting quality by measuring bifilm index. It was found that bifilm index and solidification range have an important role on the hot tearing formation. As it is known, bifilms can cause porosity and in this case, it was shown that porosity formed by bifilms decreased hot tearing tendency. As the freezing range of alloy increases, bifilms find the time to unravel that reduces hot tearing. However, for eutectic alloy (A413), due to zero freezing range, regardless of bifilm content, hot tearing was never observed. A380.1 alloy had the highest tendency for hot tearing due to having the highest freezing range among the alloys investigated in this work.

Fabrication and Properties of Al-Cu-Mg-Zn Series Alloys with Low Hot Cracking Tendency for Liquid Forging

Twelve new kinds of Al-Cu-Mg-Zn alloys with different components were designed on the basis of optimizing main alloying elements, including Zn, Mg and Cu to resolve hot crack problems of Al-Cu-Mg-Zn series alloys during liquid forging. Hot cracking susceptibility (HCS) was adopted to characterize hot cracking tendency, evaluated using constrained rod casting in a steel mould. The influence of those three main alloying elements on the hot cracking tendency and the mechanical properties of new alloys were researched. The results show that most of those new alloys have better hot crack tendency performances than 2024 alloy and 7075 alloy. The 8th alloy, Al-5Cu-4.5Mg-2.5Zn, shows best mechanical properties after liquid forging, which hot crack tendency index is the lowest, only reaching 40. The tensile strength is 327 MPa and the elongation to fracture is 2.7%, which Brinell hardness reaches 107 N/mm2.

Design and evaluation of an enhanced constrained rod casting mould for experimental characterisation of hot tearing in aluminium casting alloys

The most popular mould configuration for hot tearing evaluation of aluminium alloys, the Constrained Rod Casting (CRC) design, was evaluated via computer modelling. Filling patterns, heat flows, and shrinkage areas were assessed using the existing published design, and improvements in the design were generated. A mould of the improved design or Enhanced Constrained Rod Casting (ECRC) was fabricated and successfully used to evaluate the hot tearing tendencies of A206.2 and A380 die casting alloys. The ECRC mould reduced fill time and increased uniform filling of the constrained rods, which resulted in more uniform solidification rates for all the constrained rods. The ECRC mould and novel measurement technique predicted hot tearing in real time of A206.2 and A380 die casting alloys at initial pouring temperatures of 700, 760, and 800 °C. The A206.2 alloy exhibited hot tearing characteristics at the measurement rod while A380 did not show any hot cracking defects.

Effect of Cu Additions on Microstructure, Mechanical Properties and Hot-Tearing Susceptibility of Mg-6Zn-0.6Zr Alloys

The microstructures and mechanical properties of Mg-6Zn-xCu-0.6Zr (x = 0, 0.5, 1, 2, 3 wt.%) alloys are investigated. The effect of Cu additions on the hot-tearing susceptibility (HTS) of Mg-6Zn-0.6Zr is also studied using constrained rod casting apparatus equipped with a load cell and data acquisition system. The experimental results indicate that 0.5wt.% Cu addition into the Mg-6Zn-0.6Zr alloy shows the optimum comprehensive properties, i.e., a combination of high strength, high hardness, high hot-tearing resistance and excellent ductility. However, when Cu content reaches 2 and 3wt.%, the deterioration in mechanical properties observed is attributed to the increment in coarsened MgZnCu phase and the continuous networks of intergranular phases in these two alloys. The Cu-free base alloy had a high HTS, which is attributed to its large vulnerable temperature range and coarse grain structure, which easily caused tear propagation. In contrast, the Cu-contained alloys exhibited low HTS are due to their narrow vulnerable temperature ranges and its refined equiaxed grain structure, which effectively accommodated the stress developed during solidification. The hot-tearing fracture surfaces indicate that the hot-tearing initiated and propagated along the grain boundaries with liquid films. The results also suggest that the hot-tearing resistance can apparently be improved by increasing the initial mold temperature.

Effects of Mold Temperature and Pouring Temperature on the Hot Tearing of Cast Al-Cu Alloys

The effects of mold temperature and pouring temperature on hot tearing formation and contraction behavior of a modified Al-Cu alloy 206 (M206) have been studied. The experiments were conducted using a newly developed Constrained Rod Mold, which simultaneously measures the contraction force/time/temperature during solidification for the restrained casting or linear contraction/time/temperature for a relaxed casting. Three mold temperatures [473 K, 573 K, and 643 K (200 °C, 300 °C, and 370 °C)] and three pouring temperatures [superheat of 50 K, 100 K, and 150 K (50 °C, 100 °C, and 150 °C)] were studied, and alloy A356 was used as reference for comparison. The results confirm that alloy A356 has high resistance to hot tearing. Hot tearing did not occur for the three mold temperatures evaluated, whereas alloy M206 exhibited significant hot tearing for the same casting and mold temperature conditions. Hot tearing severity and linear contraction in alloy 206 decreased significantly with increasing mold temperature. Increasing pouring temperature increases hot tearing in alloy M206, but the effect is not as significant as that of mold temperature. The results and underlying mechanism of these effects are discussed in correlation with the thermomechanical properties and microstructures.

Roles of Alloy Composition and Grain Refinement on Hot Tearing Susceptibility of 7××× Aluminum Alloys

During the production of high-strength 7××× aluminum alloys, hot tearing has set up serious obstacles for attaining a sound billet/slab. In this research, some typical 7××× alloys were studied using constrained rod casting together with the measurement of thermal contraction and load development in the freezing range, aiming at investigating their hot tearing susceptibility. The results showed that the hot tearing susceptibility of an alloy depends not only on the thermal contraction in freezing range, which can decide the accumulated thermal strain during solidification, but also on the amount of nonequilibrium eutectics, which can effectively accommodate the thermally induced deformation. Our investigations reveal that Zn content has very profound effect on hot tearing susceptibility. The Zn/Mg ratio of the alloys also plays a remarkable role though it is not as pronounced as Zn content. The effect of Zn/Mg ratio is mainly associated with the amount of nonequilibrium eutectics. Grain refinement will considerably reduce the hot tearing susceptibility. However, excessive addition of grain refiner may promote hot tearing susceptibility of semi-solid alloy due to deteriorated permeability which is very likely to be caused by the heavy grain refinement and the formation of more intermetallic phases.

An Investigation on Hot Tearing of Mg-4.5Zn-(0.5Zr) Alloys with Y Additions

In this work, the hot tearing susceptibility (HTS) of Mg-4.5Zn-xY (x = 0, 0.4, 0.9, 2 wt pct) alloys is investigated using constrained rod casting apparatus equipped with a load cell and data acquisition system. The effect of grain refinement by Zr addition on the HTS has also been investigated. The results show that the HTS first increases with increasing the Y content, reaches the maximum at 0.9 wt pct Y, and then reduces with further increase in the Y content to 2.0 wt pct. The high HTS observed in the alloys with 0.4 and 0.9 wt pct Y is attributed to their coarse columnar grains and their large freezing ranges. The results also suggest that the resistance to the hot tearing can apparently be improved by increasing the initial mold temperature. In addition, a fine microstructure reduces the HTS. Numerical simulations using ProCAST software on HTS of Mg-4.5Zn-xY alloys are in good agreement with the experimental results.

Hot-Tearing Susceptibility of Ternary Mg-Al-Sr Alloy Castings

The susceptibility of Mg-Al-Sr alloys to hot tearing during permanent mold casting was investigated using constrained rod casting (CRC) in a steel mold. The alloys included Mg-xAl-1.5Sr and Mg-xAl-3Sr, where x = 4, 6, or 8 wt pct. The hot-tearing susceptibility (HTS) was determined based on the widths and locations of the cracks in the rods. With the Mg-xAl-1.5 Sr alloys, the HTS decreased significantly with increasing Al content. With the Mg-xAl-3Sr alloys, the trend was similar but not as significant. At the same Al content, the HTS was significantly lower at 3 wt pct Sr than at 1.5 wt pct Sr. To help understand the HTS of these alloys, the solidification path and phase fractions were calculated for each alloy. The HTS was found to increase with increasing fraction solid at the end of primary solidification.

On Transverse and Rotational Symmetries in Elastic Rods

The influences of transverse and rotational symmetries on the strain-energy functions of elastic rods are discussed. Complete function bases are presented and, for some constrained theories, these bases are also proven to be irreducible. The treatment of symmetry is based on a reformulation of a recent work by Luo and O’Reilly. It is also shown how this work relates to existing treatments by Antman and Healey for a particular constrained rod theory.

Hot cracking of binary Mg–Al alloy castings

Hot cracking of binary Mg–Al alloys in permanent mold casting was studied. The alloys contained from 0.25 to 8 wt.% Al. The hot cracking susceptibility was evaluated using constrained rod casting in a steel mold, in which cracking was induced by enlarging the ends of the rods to keep them from contracting freely during solidification. The hot cracking susceptibility was evaluated based on both the widths and locations of cracks in the resultant castings. The curve of the crack susceptibility versus the Al content showed a peak near 1 wt.% Al. The onset of hot cracking during casting was detected by connecting a load cell to a rod solidifying in a similar steel mold and recording the temperature at the end of the rod where cracking occurred. A cracking susceptibility coefficient based on the time at the onset of cracking was found to correlate well with the crack susceptibility curve.

Finite Element Method Accuracy for Wave Propagation Problems

The purpose of this paper is presentation of the results of a study concerning the accuracy of displacements caused by a single, harmonic, one-dimensional elastic wave propagating through a finite element mesh. Results are presented for the steady-state response of a finite model of the semi-infinite elastic constrained rod; both the homogeneous and two material cases were analyzed.