Hi vscid!
This is from Alcotec/ ESAB:
Aluminum/Magnesium Alloys – 5xxx Series
The aluminum/magnesium alloys (5xxx series) have the highest strengths of the non-heat-treatable aluminum alloys and, for this reason, are very important for structural applications. Magnesium (0.5 to 3.0 percent) in an aluminum weld produces a crack-sensitive weld metal composition. As a rule, the Al/Mg base alloys with less then 2.8 percent Mg content can be welded with either the Al/Si (4xxx series) or the Al/Mg (5xxx series) filler alloys dependent on weld performance requirements.
The Al/Mg base alloys with more than about 2.8 percent Mg typically cannot be welded successfully with the Al/Si (4xxx series) filler alloys because excessive amounts of magnesium silicide Mg2Si develop in the weld structure, decreasing ductility and increasing crack sensitivity... Then there is this from Alcotec also which gives a concise description of the differences between non-heat treatable and heat treatable Aluminum alloy in the form of a question:
Q - I have often heard the terms Heat-Treatable and Non-Heat-Treatable Aluminum Alloys. What are the differences between these alloys, and how does the type of base alloy affect the final strength of the weld?
A - Heat-Treatable and Non-Heat-Treatable are the two basic types of aluminum alloys. They are both widely used in welding fabrication and have somewhat different characteristics associated with their chemical and metallurgical structure and their reactions during the arc welding process.
In order to best answer your question, we first need to understand the basic differences between these two groups of alloys.
Non-Heat-Treatable Aluminum Alloys - The strength of these alloys is initially produced by alloying the aluminum with additions of other elements. These alloys consist of the pure aluminum alloys (1xxx series), manganese alloys (3xxx series), silicon alloys (4xxx series) and magnesium alloys (5xxx series). A further increase in strength of these alloys is obtained through various degrees of cold working or strain hardening. Cold working or strain hardening is accomplished by rolling, drawing through dies, stretching or similar operations where area reduction is obtained. Regulating the amount of total reduction in area of the material controls its final properties. Material which has been subjected to a strain-hardening temper, may also be given a final, elevated temperature treatment called “stabilizing”, to ensure that the final mechanical properties do not change over time.
The letter “H” followed by numbers denotes the specific condition obtained from strain hardening.
The first number following the “H” indicates the basic operations used during or after strain hardening:
H1 – Strain hardened only
H2 – Strain hardened and partially annealed
H3 – Strain hardened and stabilized
The second number following the “H” indicates the degree of strain hardening:
HX2 – Quarter Hard
HX4 – Half Hard
HX6 – Three-Quarter Hard
HX8 – Full Hard
HX9 – Extra Hard
Heat-Treatable Aluminum Alloys - The initial strength of these alloys is also produced by the addition of alloying elements to pure aluminum. These elements include copper (2xxx series), magnesium and silicon, which is able to form the compound magnesium silicide (6xxx series), and zinc (7xxx series). When present in a given alloy, singly or in various combinations, these elements exhibit increasing solid solubility in aluminum as the temperature increases. Because of this reaction, it is possible to produce significant additional strengthening to the heat-treatable alloys by subjecting them to an elevated thermal treatment, quenching, and, when applicable, precipitation heat-treatment known also as artificial aging.
Note: Because of additions of magnesium and or copper, there are also a number of silicon (4xxx series) alloys that are heat-treatable.
In solution heat-treatment, the material is typically heated to temperatures of 900 to 1050 deg F, depending upon the alloy. This causes the alloying elements within the material to go into solid solution. Rapid quenching, usually in water, which freezes or traps the alloying elements in solution, follows this process.
Precipitation heat-treatment or artificial aging is used after solution heat-treatment. This involves heating the material for a controlled time at a lower temperature (around 250 to 400 deg F). This process, used after solution heat-treatment, both increases strength and stabilizes the material.
How does the type of material, heat-treated or non-heat-treated, affect the completed strength of the weld?
In short, the difference in transverse tensile strength of the completed groove weld is governed by the reaction of the base material to the heating and cooling cycles during the welding operation.
Generally speaking, the non-heat-treatable alloys are annealed in the heat-affected zone adjacent to the weld. This is unavoidable when arc welding, as we will reach the annealing temperature, and extended time at these temperatures is not required in order to anneal the base material.
The heat-treatable alloys are usually not fully annealed during the welding operation but are subjected to a partial anneal and overaging process. These alloys are very susceptible to time at temperature; the higher the temperature and the longer at temperature, the more significant the loss of strength in the base material adjacent to the weld. For this reason, it is important to control the overall heat input, preheating, and interpass temperatures when welding the heat-treatable alloys.
Typically, the common heat-treatable base alloys, such as 6061-T6, lose a substantial proportion of their mechanical strength after welding. For example, 6061-T6 typically has 45,000 PSI tensile strength prior to welding and around 27,000 PSI in the as-welded condition. One option with the heat-treatable alloys is post weld heat-treatment to return the mechanical strength to the manufactured component. If post-weld heat-treating is considered, the filler alloy’s ability to respond to the heat-treatment should be evaluated.
Most of the commonly used filler alloys will not respond to post-weld heat treatment without substantial dilution with the heat-treatable base alloy. This is not always easy to achieve and can be difficult to control consistently. For this reason, filler alloys have been developed to independently respond to heat-treatment.
As an example, filler alloy 4643 was developed for welding 6xxx series base alloys and developing high mechanical properties in the post-weld heat-treated condition. This alloy was developed by taking the well-known alloy 4043, reducing the silicon, and adding 0.10 to 0.30 percent magnesium, thus ensuring its ability to unquestionably respond to post-weld heat-treatment.
So to answer the first part of your question, it clearly is a non-heat treatable Aluminum alloy... So let's move on to the second part of your question...
Now this is from Alcotec which is part of ESAB from Tony Anderson CEng and it is in the form of a question:
Q – I have a customer who is having problems passing guided bend tests on 5083 base material. What filler alloy should he be using and why are the bend tests failing.
A – Base material 5083 can be welded successfully with 5356, 5183, and/or 5556. All three of these filler alloys may be suitable for welding this base material, however, choosing one of these filler alloys is dependent upon the application and service requirements of the component being welded. The 5083 base material can be used in a number of applications including shipbuilding, cryogenic tanks, military vehicles and structural fabrications. From a design standpoint, considering fillet welds, the typical transverse shear strength values of these three filler alloys are 26Ksi, 28Ksi and 30Ksi for 5356, 5183 and 5556, respectively. Considering groove weld transverse tensile strength, the 5356 filler alloy is normally only used on 5083 base material when there is no requirement for groove weld welding procedure qualifications. The 5356 filler alloy may not consistently achieve the minimum tensile strength requirements of the code (40ksi – 275MPa) for groove weld transverse tensile testing of 5083 base material. The 5183 filler, developed specifically for welding the 5083 base material, will meet the mechanical property requirements for groove weld procedure qualification. The 5556 base alloy has slightly higher mechanical properties over the 5183 and can be used to weld the slightly higher strength 5456 base material, but will also meet the minimum tensile requirements for the 5083 base material. The 5083 base material should not be welded with a 4043 or a 4047 filler alloy. It not recommended that any 5xxx series base material with more than 2.5% magnesium be welded with a 4xxx series filler alloy.
Failing a guided bend test can be due to a number of reasons:
1. The most obvious reason is that there is some form of discontinuity in the weld, which has caused the break, usually lack of fusion. To determine the presence of any significant discontinuities that may have caused the failure, the failed sample needs to be inspected.
2. Was the test conducted correctly? The samples may not have been prepared correctly prior to bending, or maybe they were bent over the incorrect radius. Examination of the failed samples is necessary to verify that they were prepared in accordance with the relevant specification. The test procedure should be evaluated to determine its correctness.
3. Which testing method was used? The wraparound guided bend test method is the preferred method of testing aluminum weldments because of the significant variations in the as welded mechanical properties of some aluminum alloys. The plunger test method is not recommended for higher strength aluminum alloys like those that you are testing.
4. The use of an inappropriate filler alloy such as a 4xxx series used on this base material, could result in a weld with low ductility and therefore susceptibility to failure.
Here's another question regarding 5083 Al which may provide you with the appropriate answer you're seeking regarding the second part of your query:
Q. I have a situation were my customer is experiencing failures in their guided bend tests. The Base Metal is 5083 and the filler alloy is ER5556. The test plate is a 5mm thick single groove weld with a 70 degree included angle, no root gap and a 2mm nose. The weld is back gouged and welded from the second side. We are not sure if we are using the correct filler wire; our welding equipment supplier has suggested that we change to an ER5356 type wire. What is your professional advice on this issue?
A. What is the most appropriate filler alloy?
Base alloy 5083 can be successfully welded with filler alloys 5356, 5183, or 5556, any of these three filler alloys may be suitable for welding this base alloy. The reason to choose one of these filler alloys over the others is dependant on the application and service requirements of the component being welded. Used in a number of applications, base alloy 5083 aids in shipbuilding, cryogenic tanks, military vehicles, structural fabrications, just to name a few. The 5356 filler is normally only used on 5083 base alloy when there is no requirement for groove weld welding procedure qualifications, in accordance with the structural welding code; this is because the 5083 base - 5356 filler combination will typically not obtain the minimum tensile strength requirements of the code (40ksi – 275MPa) for groove weld transverse tensile strength. The 5356 filler alloy is often used on the slightly lower strength 5086 base alloy and will typically obtain its required minimum transverse tensile strength for grove welds (35ksi – 240MPa). The 5183 and the 5556 filler alloys will both typically meet the code tensile strength requirements for groove welds in 5083 base alloy. Developed specifically for welding the 5083 base alloy, the 5183 filler meets the mechanical property requirements for groove weld procedure qualification. The 5556 base alloy, with slightly higher mechanical properties than the 5183, will meet the minimum requirements for the 5083 base alloy. The 5556 filler alloy was developed for obtaining slightly higher tensile strength requirements (42ksi – 285MPa) of groove welds in 5456 base alloy.
In my opinion, the filler alloy selection is not the problem causing you to fail the guided bend tests; however, I do think you need to understand the application/welding standard requirements when selecting the most appropriate filler alloy.
Why then did the welded samples fail the guided bend test?
Start by considering the actual test itself and the differences between testing aluminum and other more common materials, such as steel, with this testing method.
Utilized for many years, the guided bend is a common method of testing the integrity of welds made in many different material types. The guided bend test is relatively quick and, is usually a comparatively economical method of establishing the soundness of a groove weld. Where properly used, it can be very revealing; however, in order for the test results to be of meaningful importance when testing aluminum, it is imperative that the testing methods used be thoroughly understood. There are various types of bend tests used to evaluate welds. Guided bend specimens may be longitudinal or transverse to the weld axis and may be of the root bend, face bend or side bend type. The type of bend test (root, face or side) used is determined by which surface of the weld sample (root, face or side) is on the convex (outer) side of the bent specimen and, consequently, subjected to tension load during the testing operation. Probably the most common combination of bend tests used for welder performance and welding procedure test samples are two transverse root bend tests and two transverse face bend tests per test plate.
Reasons why a welded sample may fail a guided bend test
Discontinuities in the welded joint
The most obvious reason a welded sample may fail a guided bend test is because it has been weakened by the presence of significant discontinuities. The test helps determine whether the weldment tested contains discontinuities such as cracks, lack of fusion, inadequate penetration or severe porosity. If significant discontinuities in the weldment were present, we would expect the bend test sample to fail. If inspected after testing, it is often possible to identify the type and extent of discontinuity present in the weldment.
If this were the reason for your bend test failure, you would need to evaluate your welding procedure and make the necessary adjustments to improve the weld integrity.
Using an incorrect testing fixture
The most common way to conduct guided bend testing of welded steel samples is the use of a die and plunger arrangement, often referred to as the plunger-type guided bend test fixture. Using the plunger-type guided bend test fixture for testing aluminum is not appropriate. The heat-affected zones of welds in aluminum alloys can be significantly softer and weaker than the surrounding material. If these welds bend around a plunger, the bend sample may bend sharply in the heat-affected zones and kink and/or break without adequately bending the weld metal, resulting in a test failure. In order to avoid test failures, always use the wrap around bend test fixture for testing aluminum. This testing method forces the test specimen to bend progressively around a pin or mandrel so that all portions of the weld zone achieve the same radius of curvature and, therefore, the same strain level.
Improper Sample preparation
You should be concerned about bend test sample preparation prior to bending. A common mistake is to leave the corners of the sample square. Most codes allow up to a 1/8 in. (3mm) radius on the corners of the test specimens. For best results, samples should have rounded corners, a smooth surface and be free of sharp notches that may provide stress concentration during the bending operation.
Conclusion:
With complete understanding and proper use, the guided bend test can be a very effective testing method for aluminum weldments. It is difficult to say why you are having this problem without knowing the extent of sample preparation, seeing the test samples before and after testing and knowing the testing fixture used. I hope you are able to use the information above to investigate your problem further and successfully resolve it.
Here is where you can find answers to questions related to welding:
http://www.alcotec.com/us/en/education/knowledge/qa/About The Author:
Tony Anderson is Corporate Technical Training Manger for ESAB North America prior to his current position he was the Technical Director for AlcoTec Wire Corporation. He is a Senior Member of the TWI and a Registered Chartered Engineer. He is Chairman of the Aluminum Association Technical Advisory Committee for Welding and holds numerous positions including Chairman, Vice Chairman and Member of various AWS technical committees. Questions may be sent to Mr. Anderson via e-mail at tanderson@esab.com.
Btw, here's a good link for you to look at:
http://www.alcotec.com/us/en/education/knowledge/qa/Where-can-I-find-technical-information-about-aluminum-welding.cfmHopefully this will help you out! ;)
Respectfully,
Henry
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