Showing papers on "Liquation published in 2003"

Solidification and liquation cracking issues in welding

Abstract: Solidification cracking can occur in the fusion zone during the solidification of the weld metal Liquation cracking, on the other hand, can occur in the partially melted zone during the solidification of the liquated material These two types of cracking are reviewed in this article, including the factors that affect cracking and the remedies

The effect of rejuvenation heat treatments on the repair weldability of wrought Alloy 718

Abstract: Extensive precipitation of needle- and plate-shaped δ-phase in the γ-nickel matrix of wrought Alloy 718 is the major microstructural change resulting from multiple weld repair/post weld heat treatment (PWHT) cycles. Isothermal heat treatments at 954 °C for times up to 100 h were used to simulate the multiple PWHTs in laboratory samples. Grain size did not change appreciably during these heat treatments owing to δ-phase pinning of the grain boundaries (GBs). The susceptibility of Alloy 718 to heat-affected-zone (HAZ) liquation cracking degraded as a result of these heat treatments. This degradation is due to the short time, high temperature GB liquation caused by the combined effects of δ-phase dissolution, boron carbide constitutional liquation, and GB segregation. A rejuvenation treatment (1010 °C/2 h) effectively restored the degraded weldability by removing the adverse influence of δ-phase through dissolution above the δ-phase solvus. This heat treatment also promoted a spontaneous grain refinement and increase in the fraction of special GBs owing to the elimination of δ-phase pinning of GBs. The combined effects of δ-phase, grain size and fraction of special GBs are discussed in the context of HAZ liquation cracking that occurs during repair welding of Alloy 718.

Liquation phenomena in the simulated heat-affected zone of alloy 718 after multiple postweld heat treatment cycles

Abstract: Long-term isothermal solution heat treatments were conducted to simulate multiple weld repair/postweld heat treatment cycles in Alloy 718 wrought plate. These heat treatments resulted in extensive precipitation of needle-and plate-shaped δ phase in the γ-nickel matrix. δ-phase accumulation represents the principal metallurgical damage from simulated multiple repair/postweld heat treatment cycles in Alloy 718. Grain size did not increase during this exposure due to the grain boundary pinning effect of the δ phase. Simulated weld heat-affected zone thermal cycles resulted in a variety of microstructural changes to the heat treated material, including 8-phase dissolution-promoted liquation, boron carbide constitutional liquation, and segregation-induced grain boundary liquation. The effect of these liquation phenomena on the weldability degradation of Alloy 718 is discussed.

Liquation cracking in partial-penetration aluminum welds: Effect of penetration oscillation and backfilling

Abstract: Aluminum alloys are susceptible to liquation cracking in the partially melted zone (PMZ), where grain boundary (GB) liquation occurs during welding. Liquation cracking near the weld root in partial-penetration aluminum welds was investigated. Gas metal arc welding (GMAW) with Ar shielding was conducted on binary Al-Cu Alloy 2219. Filler metals of various Cu and Si contents were used, including 1100, 2319, 4145, 4047, and 2319 plus extra Cu. The results were as follows. First, the papillary type penetration common in aluminum GMAW was observed and it oscillated up and down, resulting in a wavy weld root along the weld. Second, liquation cracking was observed in welds with penetration oscillation but not in welds without. Third, liquation cracking most often occurred in between waves of the wavy weld root. Fourth, changing the filler metal did not eliminate liquation cracking. Fifth, the PMZ grains near the weld root were deformed, suggesting that weld metal solidification induced localized tensile stress/ strain in the liquated PMZ near the weld root. Sixth, a mechanism was proposed to explain the effect of penetration oscillation: the PMZ GBs near the weld root immediately behind the oscillating penetration front of the weld pool are both in tension and liquated, and cracking can occur if liquation is significant. Seventh, highly alloyed filler metals that delay weld metal solidification (4145, 4047, and 2319 plus extra Cu) resulted in large liquation cracks backfilled with much eutectic-rich material. Eighth, a mechanism was proposed to explain the large cracks: backfilling of cracks by an abundant solute-rich interdendritic liquid from the nearby weld metal can cause melting around the cracks and worsen GB liquation and, hence, liquation cracking, which in turn increases backfilling.

Method for separating lead and antimony from lead antimony crude alloy

Abstract: The invention is a method of liquating plumbum and stibium from their rough alloy. Its character lies in that the rough alloy adopt the liquating furnace to make one or two-step liquation to produce rough plumbum. The one-step liquation is making the rough alloy of Pb>=62% further liquate to produce rough Pb of Pb<=78% adapted to electrolysis requirement. The two-step liquation is as follows: placing the alloy of 50%=

Prediction of liquation crack initiation at HAZ of laser weldment based on three-dimensional strain analysis at elevated temperature

Abstract: The purpose of this study is to develop thermal and dynamic three dimensional strain analysis method for the laser weldment in order to obtain the plastic strain at elevated temperature in HAZ of the laser weldment, and to develop the prediction method of liquation crack initiation in HAZ of laser weldment. The U-type hot cracking test was performed as an experimental evaluation method for liquation cracking susceptibility of laser weldments of Inconel 718. At the same time, thermal and dynamic three dimensional elastplastic strain analyses were performed by FEM for U-type hot cracking test specimens. Heat transfer analysis and elastplastic strain analysis for laser weldments were confirmed by experiments. From this analysis, it becomes clear that the plastic strain at elevated temperature affects liquation crack initiation in HAZ, and the critical strain at elevated temperature, which controlled liquation crack initiation, can be calculated precisely by using this proposed analysis method.