Hot-cracking in Aluminium Alloys 7050 and 7010—a Comparative Study

Warrington, D. H.; McCartney, D.G.

doi:10.1080/09534962.1990.11819040

Cited by 59 publications

(41 citation statements)

References 8 publications

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“…However, once a given alloy is 'sufficiently' inoculated (as discussed in section 4.2), further additions are not important with respect to the decrease in grain size and the alloy becomes less sensitive to cooling rate. Increasing the refiner amount may, however, influence the grain morphology [65,66] as discussed below.…”

Section: Grain Sizementioning

confidence: 99%

Macrosegregation in direct-chill casting of aluminium alloys

Nadella

Eskin

et al. 2008

Progress in Materials Science

251

148

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Semi-continuous direct-chill (DC) casting holds a prominent position in commercial aluminium alloy processing, especially in production of large sized ingots.Macrosegregation, which is the non-uniform chemical composition over the length scale of a casting, is one of the major defects that occur during this process. The fact that macrosegregation is essentially unaffected by subsequent heat treatment (hence constitutes an irreversible defect) leaves us with little choice but to control it during the casting stage. Despite over a century of research in the phenomenon of macrosegregation in castings and good understanding of underlying mechanisms, the contributions of these mechanisms in the overall macrosegregation picture; and interplay between these mechanisms and the structure formation during solidification are still unclear. This review attempts to fill this gap based on the published data and own results. The following features make this review unique: results of computer simulations are used in order to separate the effects of different macrosegregation mechanisms. The issue of grain refining is specifically discussed in relation to macrosegregation. This report is structured as follows. Macrosegregation as a phenomenon is defined in the Introduction. In Part 2, direct-chill casting, the role of process parameters and the evolution of structural features in the as-cast billets are described. In Part 3, macrosegregation mechanisms are elucidated in a historical perspective and the correlation with DC casting process parameters and structural features are made. The issue of how to control macrosegregation in direct-chill casting is also dealt with in Part 3. In Part 4, the effect of grain refining on macrosegregation is introduced, the current understanding is described and the contentious issues are outlined. The review is finished with conclusion remarks and outline for the future research.

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Section: Grain Sizementioning

confidence: 99%

Macrosegregation in direct-chill casting of aluminium alloys

Nadella

Eskin

et al. 2008

Progress in Materials Science

251

148

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“…Ring molds 1 2 and cold finger molds 112 are examples of molds in which the developed stresses are perpendicular to the direction of solidification. The ring mold consists of a ring and a core with the same central axis, both resting on a flat plate.…”

Section: Hot-tearing Testing Methodsmentioning

confidence: 99%

Influence of zirconium and scandium on the microstructure, tensile properties, and hot-tearing susceptibility of Al-2WT%Cu-based alloys /

Nabawy¹

2010

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In the second alloy category, seventeen alloy compositions were prepared, using different additions of Zr, Sc, Ti-B, Sr, Ag, and Si These alloys were further divided into four groups, namely, the Zr-Ti, Zr-Sr, Zr-Sc, and Si alloy groups. Tensile test bars (cooling rate 7°C/s) prepared from these alloys were solutionized for 8h at 490°C then age-hardened at temperatures of 180°C and 220°C for aging times of 2, 4, 6, 10,16, 24, and 48h, and 0.5,1, 1.5, 2, 4, 6, 10, 16, 24, and 48h, respectively. It was observed that combined additions of Zr-Ti Zr-Sr, or Zr-Sc refined the grain size of the base alloy considerably, from 219 um to 104-46 urn, since these elements form primary trialuminide intermetallics including Al3(Sci-x Zr x ), Al3(Sci-x -yZr x Tiy), and AlaZr which act as nucleation sites for o-Al grains, thereby producing fine non-dendritic structures. The refined non-dendritic morphology produced by the combined additions of Zr-Ti Zr-Sr, or Zr-Sc caused a reduction of about 65% in the amount of the AliCu phase in the base alloy, and a reduction in porosity of about 50%. The addition of 2 wt% Si also produced the same reduction levels in the amount of AfeCu and porosity, brought about by the increase in the Al-Si eutectic content. Age-hardening peaks were observed after aging for lOh and 24h at 180°C, and after aging for Ih and 2h at 220°C. The Zr-Sr and Zr-Ti alloy groups displayed the highest level of improvement in the tensile properties of the Al-2wt%Cu base alloy followed by the Zr-Sc and Si alloy groups, in that order. The 0.02wt%Sr-0.7wt%Zr containing alloy produced the highest ultimate tensile and yield strength values of 383 MPa and 326 MPa, respectively, after 4h of aging at 180°C. The strength of the base alloy increased in the Zr-Ti alloy group with an increase in Zr content from 0.15wt% to 0.7wt% after aging at 180°C for lOh. This increase may be variously attributed to Al$Zr and Al3(Zri. x Ti x ) dispersoids acting as heterogeneous nucleation sites for age-hardening phases; to the modifying action of Zr on the S' (AfeCuMg) phase; and to the action of Zr-Ti in producing a refined non-dendritic grain structure. Combined additions of Zr-Sr and Sr-Ti displayed the best elongation levels of all the alloys investigated, as witnessed by the 0.02wt%Sr-0.15wt%Ti-containing alloy and, 0.02wt%Sr-0.7wt%Zr-containing alloy. These improved levels may be the result of the modifying effects of Sr on o-Fe particles, as well as of the roles of Zr and Ti in producing a fine non-dendritic os-Al structure. The 0.02wt%Sr-0.15wt%Ti-containing alloy displayed the highest resistance to softening during aging at 220°C because of the respective modifying and refining effects of Sr and Ti on the microstructure.

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“…A wider temperature range of the mushy zone and a longer time interval of the film stage may increase the tendency of hot tearing [27-30, 35, 46, 47]. Refined grain size and equiaxed dendrite morphology could reduce the susceptibility of hot tearing [27,29,30,32,35,47,48,49,50]. Higher pouring temperature and casting speed favor hot tears, while molds or core forms and the like are influenced by changing contraction conditions.…”

Section: A C O B%mentioning

confidence: 99%

modeling of hot tearing in aluminium alloy /

Wu¹

2003

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Hot tearing is one of the "universal" defects in many aluminium casting products. The formation of hot tearing involves complex solidification phenomena and processing conditions. During the DC casting process, it often initiates at the surface and propagates towards centre. In the present work, a coupled solidification model (microstructure) and hot tearing model has been developed in order to predict the hot tearing susceptibility of aluminium alloys and thus to better control its occurrence.The microstructure modeling in this project was progressed from two-dimensional simulation of Al-4.5%Cu binary alloy solidification, and the modeling results were compared with the experimental data. The information provided by the microstructural model, such as temperature field, evolution of solid fraction, the final grain size and the microstructure morphology, is essential for the further study of hot tearing.In order to predict the hot tearing susceptibility during solidification, two hot tearing criteria with different aspects have been implemented into the microstructural model. The Lahaie Bouchard (LB) criterion is based on the mechanical response of the semi-solid body, while the Rappaz Drezet Grenaud (RDG) criterion considers the pressure drop from both thermal deformation and solidification shrinkage through the mushy zone.In the microstructure -hot tearing model using LB criterion, by combining the constitutive law that reflected the viscous behaviour and the critical fracture based on the capillary force, a critical strain can be calculated to identify when and where hot tearing 11 could occur. The critical strain is influenced by cooling condition, strain rate, solid fraction and alloy composition. The modeling results give an overall indication of the appearance of hot tearing, and can be used to investigate the susceptibility of hot tearing tendency influencing by the solidification parameters and the thermal properties of the Al-Cu alloys.To valid the coupled microstructure-hot tearing model, some experiments have been carried out on the Direct Chill Ingot Surface Simulator (DCSS). The displacements under applied tensile loads were measured and the occurrence of the hot tearing was observed.The results from modeling and experiments were compared and discussed. The complete microstructure -hot tearing model (with the LB criterion), corresponds with the facture stress range found in the experimental data. By further correction based on a recently modified constitutive model, the critical strain range between the modeling and experiment can give better agreement to identify the appropriate condition for the susceptibility of hot tearing.The modeling results from the RDG criterion showed that it is more suitable for the central type of hot tearing. It needs to be studied further to know whether this criterion is applicable for the surface hot tearing as in the case of DC cast sheet ingots. Ill ACKNOWLEDGEMENTSIt is with great pleasure that I acknowledge all those who were involved directly or indirectl...

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Hot-cracking in Aluminium Alloys 7050 and 7010—a Comparative Study

Cited by 59 publications

References 8 publications

Macrosegregation in direct-chill casting of aluminium alloys

Macrosegregation in direct-chill casting of aluminium alloys

Influence of zirconium and scandium on the microstructure, tensile properties, and hot-tearing susceptibility of Al-2WT%Cu-based alloys /

modeling of hot tearing in aluminium alloy /

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