Improvement in Mechanical Properties of A356 Tensile Test Bars Cast in a Permanent Mold by Application of a Knife Ingate

Abstract

As a standard test-bar permanent mold, the ''Stahl'' Mold has been widely used in foundries to assess the properties of cast alloys. However, inferior mechanical properties are often obtained with this mold due to shrinkage-induced microporosity in the gage section. In order to improve the mechanical properties, a design modification comprising a thin knife ingate between the feeder and test-bar cavity was evaluated in this work. The new design was studied by computeraided simulation. Simulations predicted that the knife ingate improved the metal feeding capability and reduced the shrinkage microporosity at the gage section from 3 to 1 pct. Experimental verification work has been undertaken with aluminum alloy A356, and the results were analyzed by a statistics theory-based factorial analysis method. The new design resulted in main effects with ultimate tensile strength (UTS) improvement of 20 MPa (relative 12 pct) and elongation increment of 2 pct (relative 45 pct) for the as-cast test bars.

Optimization of a Permanent Step Mold Design for Mg Alloy Castings

“…Lower shrinkage porosity in the thinnest step can be referred to the good metal filling capability, which in turn may be attributed to the application of the thin and large fan-type ingate connecting the runner and die cavity. Wang et al [8] obtained similar porosity reduction in the Stahl permanent test-bar mold by applying a thin ''knife'' ingate on the test bars. Such ingate configuration is similar to the fan ingate suggested in the current work.…”

“…However, to overcome the difficulty in producing the best mechanical properties of cast alloys, [5] several efforts have been paid by foundries to improve the initial Stahl design. [6][7][8][9] Furthermore, because the test bars obtained by the Stahl mold show well-defined dimensions, in terms of gauge length and section, this configuration does not allow to reproduce different solidification conditions integrated into a single die design.…”

Evaluating the Tensile Properties of Aluminum Foundry Alloys through Reference Castings—A Review

“…However, the study was limited to microstructural characterization of magnesium alloys and needs to be extended to aluminum alloys. By means of numerical simulation techniques, Wang et al [ 31 ] found that the gauge section of the standard Stahl mold (standard ASTM B-108) showed higher porosity (about 3%) compared to the AA Step mold (less than 1%) in an AlSi7Mg alloy. This comparison confirmed the statement of Singworth and Kuhn [ 32 ] that the Stahl mold could not produce better mechanical properties than the Step mold, due to higher micro-porosity in the gauge section on account of micro-shrinkage.…”

Reference Dies for the Evaluation of Tensile Properties of Gravity Cast Al-Si Alloys: An Overview

“…Figure 8. Comparing the porosity in (a) ASTM mold and (b) modified design, estimated using numerical simulation; (c) arrow shows modified riser thickness [20] (d) Details of the knife ingatecasting and (e) the improvement in the tensile properties[21] …”