Update on Zinc Die Casting
Research & Development
Dr. Frank E. Goodwin, Vice President, Materials & Science
International Lead Zinc Research Organization, Inc.
Research Triangle Park, North Carolina
Introduction 180
Since 1958, the International Lead Zinc Research Organi- 160 1% strain
zation, a cooperative, not-for-profit organization initially 140 Failure
funded solely by lead and zinc miners and smelters world- 120
wide, has supported the zinc die casting market by con-
100
Hours
ducting research on product and process issues of interest
to zinc die casters. These projects over the years have 80
developed improved plating and other finishing processes, 60
discovered new alloys, written the first mathematically- 40
based die design programs that are now widely used, char- 20
acterized mechanical and corrosion properties of casting
0
alloys and developed design tools to aid the customer.
5 ZA8 4 15 16 16B 17 26 27
This article will review the status of two ILZRO
research programs currently underway along with several Alloy
recently developed tools that are now available for die • Time to rupture (dark bars) & time to 1 percent creep strain in tested zinc
alloys at 140°C (285°F) and 31 MPa (5100 psi)
casters and their customers. These are all helping to sup-
port markets for zinc die castings. Overall direction to • Commercial alloys 5 and ZA-8 are shown in the set of bars to the left.
ILZRO’s research efforts have been given by a succession • All results are average of 3 tests
of Zinc Casting Task Forces, organized periodically to Fig. 1 – Average Creep Performance Comparison (140°C & 31 MPa).
review the results of ILZRO programs, identify important
future needs, and prioritize research efforts. A summary several of the new alloys developed are surviving between
of a survey carried out by PERA (UK) to support the 60 and 80 hours, with the highest performing alloy endur-
activities of the most recent Zinc Castings Task Force ing for 160 hours before failures occur. Times to 1 percent
was given in the June 2002 issue of NADCA’s LINKS strain, a more practical engineering criterion, are between
magazine. This confirmed ILZRO’s current directions of 10 and 20 times higher for these new alloys compared with
research which are aimed at extending the capabilities of Alloys 5 or ZA-8. The most promising composition range
zinc die castings by two major thrusts: development of for these alloys contains Al between 5.5 and 7 percent,
hot chamber die castable zinc alloys with improved high copper between 2.4 and 3.6 percent, titanium between 0.1
temperature performance (specifically, creep resistance) and 0.75 percent, and boron between 0.0004 and 0.004
and development of designs for zinc die cast heat sinks. percent. These ranges will be further optimized in a cur-
A summary of each of these projects is given below, fol- rent set of experiments. These alloys also show very good
lowed by a description of recent tools for market devel- compatibility with hot chamber shot and equipment. Little
opment and technical support that have grown out of attack has been seen in samples of H13 or P20 die steel
ILZRO’s past research. exposed to this composition range for several hundred
hours. This alloy range is also showing a promising range
Creep Resistance Zinc Alloy Development of tensile and yield strengths, together with elongation
Beginning in 2000, the U.S. Department of Energy Cast behavior similar to that found in conventional hot chamber
Metals Coalition, of which NADCA is a key member, die cast zinc alloys. As part of the Department of Energy-
authorized 50 percent funding for a program to develop funded work, ILZRO will engage in a technology transfer
a new generation of high creep resistant zinc alloys. The effort with cooperating die casters during 2003. Any die
other 50 percent of funding is mainly supplied by the zinc caster, or die casting customer interested in conducting
industry, along with prominent independent zinc alloyers. trials with alloys found as a result of this program is urged
A designed experiment is determining the effect of 10 ele- to contact ILZRO or NADCA.
ments on the creep properties of zinc alloys: Al, Cu, Mg,
Li, Cr, Ti, B, Ce, V, and Si. A large number of these alloys Designing Zinc Die Cast Heat Sinks
have been fabricated, and analysis techniques developed for Electronic Applications
to determine their composition, after creep testing, die Electronic devices are becoming increasingly miniatur-
fluidity testing, and mold attack testing have been carried ized, leading to increased demands for heat removal from
out. As shown in Figure 1, results to date are promising densely packed electronic devices. Traditionally, heat sinks
– whereas alloys ZA-8 and 5 can survive no longer than have been manufactured from copper or aluminum extru-
three hours at 140°C under a stress of 31 MPa (4500 psi), sions or other fabricated forms. It is not obvious, and
28/DIE CASTING ENGINEER March 2003 www.diecasting.org/dce
fasten zinc die castings to other components. This fastener
Fig. 2 – Die-cast zinc alloy relaxation, a manifestation of compressive creep, has now
heat sink used in “Pixel Flow,” been thoroughly characterized, allowing a set of design rec-
the world’s fastest graphics ommendations to be made for predicted long term clamping
supercomputer. (Courtesy loads. Factors such as thread pitch (threads per inch), screw
Prof. K. Keller, Univ. of North length, screw diameter, boss geometry, thread type (tapped
Carolina).
or self-tapping), and other factors all contribute to a fasten-
comes as a er’s long term clamping load ability. This Web-based tool
surprise to many designers that the thermal con- is available through through one of the International Zinc
ductivity of the metal from which the heat sink is made Association’s (IZA) Web site initiatives: www.dezign.org.
is not the limiting factor in heat dissipation. Rather, the One of the main advantages of zinc die castings compared
transfer of heat from the surface of the heat sink to the with other manufacturing techniques is its ability to produce
surrounding air governs the rate of heat removal. Under high tolerances. These are clear from the tolerances indicated
ILZRO sponsorship, a program to determine optimum in the NADCA product standards and the capabilities of die
designs for zinc die castings has been carried out and a castings are being extended as die casters learn how to pro-
computer program produced, allowing appropriately sized duce dies, and operate die casting machines, under conditions
heat sinks made in zinc die castings, to be recommended that consistently produce these tolerances. Recognizing this,
for normally encountered heat dissipation requirements. ILZRO commissioned a manual by two die casting experts,
The ability of zinc die casting, compared with aluminum Bill Walkington in the USA and Jim Birch in the UK, which has
or copper extrusions, is the freedom of geometric design now been produced as a CD distributed through NADCA.
that can be practiced. This opens up possibilities for The manual describes current worldwide standards for preci-
improved heat dissipation in many applications. Also, the sion end die casting followed by factors of die building and die
thicknesses to which zinc die castings can be produced, design that influence tolerances that can actually be achieved.
down to less than 0.75 mm (0.030 inches) allows very Die casting production practices that minimize variability are
high surface areas to be obtained with minimum masses then discussed, including overall production planning and exe-
of metal, overcoming zinc’s higher density in comparison cution and record keeping. This is followed by a description of
with aluminum. A recently designed high performance the most commonly encountered zinc die casting defects and
heat sink is shown in Figure 2. how they can be cured. The manual concludes with a descrip-
In the computer tool that has been developed, the tion of rapid prototyping methods that have proven successful
user can specify the shape and size of the heat sink, the in development of zinc die casting applications.
zinc alloy from which it will be made, the surrounding It is intuitive to many people that zinc die castings have a
air speed and the air temperature. The user will specify high damping capacity, based upon the lack of “ringing,”
either the base temperature, or the heat dissipation rate. a zinc die casting will emit when struck, compared with
The program will calculate and provide as output the other metals. Zinc alloys do have high damping capacities
one of these two variables that is not specified. Output compared with other metals, however this property has
information includes calculated heat transfer coefficient, yet to be exploited in many applications. To aid designers
base temperature or dissipation rate, temperature profile in their efforts to take advantage of zinc’s damping prop-
through the fins, and the overall thermal resistance (sink erties, ILZRO has recently produced a manual describing
performance). In heat sink design, it is important to mini- damping phenomena in zinc die castings and how they can
mize contact resistances between various components. be taken advantage of. This includes effects of frequency,
The ability of a zinc die casting to combine the function temperature, excitation amplitude, and other factors. The
of many components into one eliminates such contact effects of die casting shape, thickness, and location in the
resistances, improving heat dissipation performance. assembly are described. An automotive case study involving
Recently Developed Publications and Tools an accessory bracket applies all these principles, showing
the reduced in-the-age (noise vibration and harshness)
A frequently asked question about zinc die castings relates properties that can be obtained through application of zinc
to the clamping load of steel fasteners (screws or bolts) that die castings is available from ILZRO at www.ilzro.org.
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